One thing I don't understand about lectures is why the lecturer covers the material that is already presented in the book and assigned as reading material to the students.

Is the assumption that some students are actually incapable of reading? If not, what then is the point of covering the same stuff in the lecture? Imagine that reading the book is a lecture itself: what then is the point of giving two identical lectures?

I understand that some students may not understand the book, and a spoken lecture makes it possible to answer questions and provide clarifications on unclear statements from the book, or just to add more detail/intuition to a certain topic.

But, truth be told, those parts of a lecture make up a small, small minority. Most of the lecture is indeed spent on just repeating what the book said - except of course with much less detail, since you can't cram 30 pages of written words in a 1 hour lecture.

So would it not be much more efficient to do it differently? Here's one example for a 1 hour lecture, but you can think of your own:

  • Spend the first 15 minutes on recitation of the book material. It gets everyone on board, sets the tone, refreshes everyone's mind. During these 15 minutes, certain added remarks can be made if the lecturer feels them necessary.
  • Spend the next 10 minutes answering questions by confused students.
  • You now have 35 minutes left to cover extra material not presented in the book. This could be in-depth examples or intuition of the topic just covered, advanced extensions, or just some extra topic that you wouldn't have time to otherwise cover in your course.

This way you are both more efficient since you are not wasting time repeating stuff, and you also take care of students' questions and get some time to add clarifying remarks. You get the best of both worlds.

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    In some cases, most of the students don't read the assigned material, or just skim over it.
    – Bitwise
    Commented Jul 12, 2018 at 7:55
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    For the same reason they don't (normally) assume that all students are perfect copies of the professor: it's an obviously false assumption.
    – Ink blot
    Commented Jul 12, 2018 at 8:20
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    What if there is no single book? My courses are typically blends of multiple sources. Commented Jul 12, 2018 at 8:55
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    @henning I think there is a chicken-and-egg situation here. The lectures are built this way because the students don't read the material, and students don't read the material because the lectures are built this way (well there are probably other reasons also at play).
    – Bitwise
    Commented Jul 12, 2018 at 11:19
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    @Makeo If the goal is to educate students, professors must focus on what students actually do, i.e. at best skim the material, rather than what they ought to do.
    – Bob Brown
    Commented Jul 12, 2018 at 12:56

14 Answers 14


The answer may depend on what type of course we are talking about, here I'll focus on STEM.

The most obvious answer would be "because it would be a false assumption". Many students don't read the books. But then you get to the question: why don't the students read the books?

I'm an engineering student, and here's my perspective: in STEM courses it's quite often the case that the lectures are quite simply a boiled-down version of the books; they present the same theorems as the books, in the same order, often using the same examples, but without all the "fluff". Students don't read the books because we go to the lectures, take notes, and get all the necessary material in a document we wrote ourselves. Writing it ourselves helps us learn the material, and since it's a boiled-down version it's much less material to read through when preparing for exams.

As for professors, if they assume that the books have been read and understood, they wouldn't have much to talk about since what they planned to present was the book's material. They could use lectures for Q&A sessions and practice problems but attendance would be quite low in that case and students would complain about paying for simply being told what book to read instead of being presented the material. Besides, (at least in the case of my university) Q&As and practice problem sessions are typically done by the TAs on a regular basis anyway.

I imagine this may not hold for other types of classes such as history or literature in which documents are assigned to be read and then discussed and analyzed in class, but I have little to no experiences with those so I can't give an informed answer.

P.S: "Imagine that reading the book is a lecture itself". Fun fact: the word lecture is french for reading.

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    There is also the fact that some people are auditory and some are book learners. Lectures appeal to one of those, books to others.
    – enderland
    Commented Jul 12, 2018 at 15:55
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    @ElysianFields: There is no evidence that's a real thing: danielwillingham.com/learning-styles-faq.html Commented Jul 12, 2018 at 19:09
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    @DanielR.Collins perhaps my wording was not precise enough but acting as if 100% of students will have the same learning affinity towards readings and lectures seems.. a stretch. People are different in their abilities (or disabilities) and preferences.
    – enderland
    Commented Jul 12, 2018 at 19:45
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    @Elysian "I feel like this should be different" is the opposite of science. The linked article references a review on the topic (Pashler, H., McDaniel, M., Rohrer, D. & Bjork, R. 2008. Learning styles: Concepts and evidence. Psychological Science in the Public Interest, 9, 106-119) which claims to not have found any studies that demonstrate your claim. But if you have convincing studies that show a difference I'd love to read them as well. It is an interesting topic.
    – Voo
    Commented Jul 13, 2018 at 7:24
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    @Voo you're telling me people who are deaf or have reading disabilities learn the same? I have a close friend who is dyslexic. He struggles a lot reading. Are you saying there is research that shows someone who is dyslexic or deaf learn just as well in either mode? I would love to show that research to my friend to help him realize he can learn via reading just as well as via listening.
    – enderland
    Commented Jul 13, 2018 at 13:58

I think that Flipped classroom is what you are looking for. Flipped classrooms are designed for students to prepare the material by themselves and devote lecture time to exercises, debates and questions.

I have heard about Flipped classroom implementation in university courses but I have never taken any myself. Personally, I find more appealing the idea of using lecture time for debates and exercises rather than expanding on the material. It gives the opportunity to go over what students have read and to put it into practice, reinforcing their knowledge. Every student can read and listen to the lecturer but fully grasping the material goes beyond that.

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    In theory flipped classrooms are great, in practice they can be a way for the lecturer to hide his/her inexperience with the material.
    – bendl
    Commented Jul 12, 2018 at 18:23
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    The flipped classrooms require a level of discipline from the students and the lecturer. Students which (think that) they don't have enough time to truly understand books (understanding a page can take several hours!), which are under pressure from homework and other 6 subjects they have this semester, might not dedicate enough time to prepare for the lecture. If the students (or at least the majority of students) did not prepare for the lecture, then flipped classroom is wore than regular lecturer talking at the audience which might or might not pay much attention.
    – AndrejaKo
    Commented Jul 13, 2018 at 7:02
  • @AndrejaKo It is true that flipped classrooms would not work if students do not prepare. However, I think that knowing they are expected to use the material in the lecture instead of just listening is an incentive for them to prepare. Having said that, I admit that flipped classrooms demand more work from the lecturer and that they would work better is small classrooms where students would know they would be indeed required to participate.
    – fa__
    Commented Jul 13, 2018 at 7:53
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    @bendi I think that depends. Answering questions and preparing exercises can be more challenging than reading slides aloud.
    – fa__
    Commented Jul 13, 2018 at 7:56
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    @bendi well yes thats what one would think. But in fact flipped classroom really needs the teacher to be even more prepared and even better informed. Since the teacher is now in a position where he needs to be able to steer the class home form uncharted waters. Try it it is surprisingly challenging.
    – joojaa
    Commented Jul 13, 2018 at 22:00

It depends on the course. If I'm teaching a course on standard undergraduate material, I'm using a textbook that contains most or all of what the students need to know. So I'm not sure what would go in the 35 minutes of extra time you suggest. (There's plenty of extra stuff I could talk about that would make the lectures more interesting for me, but it's doubtful that this would be helpful for anyone else.)

The goal is not to cover as much material as possible, it's to cover the material thoroughly enough that the students will actually learn it. Seeing the material once isn't enough to understand it, and 15 minute refresher at the beginning of the lecture would be insufficient, even if all the students did read the book.

For a graduate course or a higher-level undergraduate course, the kind of thing you suggest is fine, and commonly done.


I agree with you that lecture time (i.e. face to face time) is often badly used. Copying my notes to the board so that you can copy them to your notes seems (and is) foolish, unless the course is absolutely unique and I'm the only resource. The joke is that while this copying is going on, the information goes through the mind of neither.

However there are a few reasons to explain this. The lesser reason is that instructors try to be realistic in their explanations about what students do (and don't do). So they try to present a coherent picture of a topic, rather than just answer questions helter-skelter.

A more important reason is that the book itself doesn't tell the whole story and a good lecturer will, as part of that coherent picture, fill in additional ideas and, most important, insights. Many topics are actually insight-driven and it can be hard to capture that in print.

A still more important reason, however, is that different people learn differently. The term of art is "learning modalities". Some people learn fine by reading, others by seeing, or hearing, or interacting, or practice, or ... So a good use of face to face time is to "ping" the students with preferred modalities other than book reading.

But your bullet point description of a better way, is very good. You also need to get the students to practice the art, what ever it is. Sometimes this is done within a lecture period so that you can give immediate guidance (or use pairing so the students can help each other. But usually you end by sending them off to some active task (and more readings, of course). In fact your final 35 minutes might well be spent in having the students practice. This is called active learning and is an extremely important modality and generally a good use of at least part of "class time."

In fact a better use of class time is to do only those things that can only be done face to face. For the last several years of my teaching (retired now) I never lectured in the sense of writing things on a board (or showing slides) that students were expected to copy. We did group work (sometimes paired), active demonstrations (sometimes with student "actors"), academic games (think Jeopardy), etc. Students would have outside reading, but even then, most of their work was active practice of some skill.

An historical note: Charles University (Prague) was founded about a hundred years prior to the invention of the printing press. Books were very expensive if they even existed. Lectures then, were an efficient way to spread knowledge. But what was optimal then is past its "use by" date, perhaps.

  • "The book doesn't tell the whole story", uhm, right, but the running assumption is that the lecturer spends most of their time repeating the same story the book is telling. So how are we any better of?
    – Makeo
    Commented Jul 12, 2018 at 12:08
  • @Makeo, as we agree, it isn't. There are better ways. Your post is a start.
    – Buffy
    Commented Jul 12, 2018 at 12:12
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    Btw, studies have shown that hand writing notes improves retention over "passive" listening.
    – industry7
    Commented Jul 12, 2018 at 15:39
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    @industry7, I've made similar claims in other fora. Can you provide any reference to these studies. I also think that hand written notes are preferable to real-time typed ones, but that is a different idea.
    – Buffy
    Commented Jul 12, 2018 at 15:44
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    @industry7 I find that ridiculous. Who says passive listening is the only alternative to writing? Active listening is the superior alternative to both. Lecturers that force their students to into writing notes miss the point. Copying is a passive action that redirects the student's focus to rote physical activity. This attention could be much better spent actively. How to force students to be active listeners? Begin by learning to teach! Commented Jul 13, 2018 at 9:49

There was a psychologist named Hermann Ebbinghaus that introduced the idea of a forgetting curve. In a nutshell, after an extremely short period of time you will begin to forget about things you have read or heard in a lecture.

While reading part of your textbook in preparation for class is important, you need spaced repetition to increase the amount of what you remember on a topic. The class period is a good way to add a "spaced repetition" and ask the lecturer about anything that is unclear from your reading.


This will vary a lot by level.

I concluded at one point that, in "remedial" type courses1, many students are not able to read the textbook. And, therefore, the lecture was best used to help the students in reading the textbook.

Here is the definition given in the textbook. What does this phrase mean? What does that notation mean? How is this related to what we did last week? Let's do some examples that illustrate it.

1which, in my university as far as mathematics was concerned, included a large percentage of the incoming students: students who "chose" to take as little math as possible in high school.

  • Please say more. Too many times the "lecture" is just writing out the textbook (or nearly that) one line at a time. No progress is made.
    – Buffy
    Commented Jul 12, 2018 at 14:40
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    "Not able to read the book" is not the same as "Not able to read the words and sentences in the book". Many university entrants (at least in STEM subjects) will have had zero experience and practice at reading an entire technical book, as a method of learning the information it contains. "English comprehension" exercises based on half a page of text about some random topic don't count for much as preparatory training for that skill, IMO.
    – alephzero
    Commented Jul 12, 2018 at 15:40

Lectures are used to enhance what you learned from reading. They are used as a way to help guide interpretations on the material in the books. Most of my professors emphasized this a lot (especially in the STEM courses) during my time in school. The professor takes time to focus on the main focus of the material often glancing over the peripheral information provided in texts to ensure that the students are getting to the base of the course. The redundancy is meant to help students retain the information as well.


Many students lack the discipline and/or commitment to devote themselves to a completely unknown subject. Instilling such work habits and essentially making the students independent is a major part of the school experience. In its extreme form, in grad school, students are expected to perform research by themselves, guided by the mentor, but still largely by themselves.

Students are also often inexperienced when it comes to extracting the important things from lectures. The professor can of course talk about only a limited amount of things from the book during the lecture, but these are the crucial parts of the subject. Think of it as a steel structure, which can stand on its own and provide students with the crude basics, but can also later filled in with walls, floors, windows, etc. as the students further study the matter. In other words, it gives them a framework for further study.

Finally, there is the scope. The contents of a course a covered in the literature for it, i.e. the book. The professor tries to convey those contents in a manner that would enable his students to absorb as much of the matter as possible, ideally so that the book can only be read through to fill in the gaps or even to realize that nothing new is in the book.

On the other hand, people who don't have access to the professor or the university can still learn the same things by going over the literature, same as with students who refuse to attend lectures. From experience, this is usually the much much harder way.


Usually the lecture is reserved for the most important material... As you point out, lecture time is more costly than book space. So if it is important enough to lecture on, then why wouldn't you also include it in the book?

If you lecture for 35 minutes on extra material (genuinely not covered by the book), then you will probably want to make that material available in a printed format. Even if you don't care about the poor student who got sick and missed it, you probably care about the student who diligently came to class and took notes but who didn't perfectly transcribe everything into their notes since they were trying to understand brand new material while taking notes. Since it's so much material, you might even decide to publish it as a bound copy, with pretty figures and nice problem sets for students to work in order to check their understanding. If you're really lucky, you have actually already written a textbook on the subject (or know someone who has), so instead you amend this material into your textbook... Now you're back at square one.


Disclaimer: I'm not an experienced teacher, and I certainly don't represent all lecturers, so this is mostly just guesswork based on my experience in academia.

Edit: Just to clarify, I'm not claiming that what lecturers do now is optimal, I'm just explaining why they are doing it now. However, planning and executing a good and pedagogical course from scratch requires a lot of time and effort that might not be available to many university teachers, even if they were motivated. So the current method may indeed be a "local" optimum in many cases.

Lecturer's job is to help the students learn as well as he can in the time given to him. In an ideal world, the students would do everything as the lecturer has planned, but experience has told us that this is not what happens. So the lecturer needs to adapt.

I've been TAing a course where the lectures start by a small quiz about the contents of that lecture. The quizzes aren't graded, but you get some extra points by attending a lecture (on time), so the students have some motivation to do it. And the results vary from end to end. A few students seem to know everything the course wants to cover, and a few students seem like they haven't even heard about the things in the course, and the rest are anything in between.

Why? Is the assumption that some students are actually incapable of reading? If not, what then is the point of covering the same stuff in the lecture? Imagine that reading the book is a lecture itself: what then is the point of giving two identical lectures?

The assumption is not that they are incapable, the assumption is that they are not willing to learn everything just by reading a book, for good or bad reasons. Lecturers often have chosen to target their lectures to people who, for one reason or another, prefer not to learn stuff only by reading a book. Beause students who learn well enough by reading the book don't really need lectures as much as the ones who don't.

Even the worst lecturers I have seen don't just recite the book. They allow questions and try to explain things in their own way. Another point of view often helps you if you didn't understand what the book said.

And if the lecturer's quality of teaching is so low that they really just recite the book without adding anything, I don't think the problem is the structure of the lecture, it's their motivation, skills, or time constraints.

So would it not me much more efficient to do it differently? Here's one example for a 1 hour lecture, but you can think of your own:

  • Spend the first 15 minutes on recitation of the book material. It gets everyone on board, sets the tone, refreshes everyone's mind. During these 10 minutes, certain added remarks can be made if the lecturer feels them necessary.

Earlier you said you can't even cover everything in the book during one hour. So everyone who has not read the book or has not understood something will definitely not understand anything here.

  • Spend the next 10 minutes answering questions by confused students.

From my experience, at this point the questions would be anything between "no questions" or "I didn't understand anything" (which looks like "no questions"). If someone has a real question about one part, I don't see how this is any better for them than asking it while the lecturer is teaching that part in the 1 hour lecture.

  • You now have 35 minutes left to cover extra material not presented in the book. This could be in-depth examples or intuition of the topic just covered, advanced extensions, or just some extra topic that you wouldn't have time to otherwise cover in your course.

Books are designed to contain material that is suitable for one course, and I'd assume lecturers want to teach the material they currently have in the course. So they would probably want to spend this 35 minutes going over the material they explained in the first 10 minutes, but in more detail. So this would be like the usual book lecture you described, just structured in a different way.

This way, you are both more efficient since you are not wasting time repeating stuff,

But repeating stuff is pretty much required for learning. Yes, you get repetition when you do exercises, but reading a book and listening to a lecture about the same things is another way of learning.

but you also take care of student questions and get some time to add clarifying remarks.

Are you saying that your lecturers don't allow student questions during the lecture? I have seen lecturers ranging from horrible to excellent, but I've never met one who does not enjoy when a student asks a question during the lecture.

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    "even the worst lectures...": I have seen many lectures where the lecturer just copied a text (sometimes a book, sometimes their lectures notes) on the blackboard, without explaining anything more or allowing questions.
    – Udank
    Commented Jul 12, 2018 at 9:04
  • @Udank I know I've been lucky with my teachers, so that's why I added the next paragraph; would you agree with that?
    – JiK
    Commented Jul 12, 2018 at 12:14
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    In my experience, (good) books about any subject cover much more than is remotely possible to cover in a typical course. The "use extra time to discuss what the book doesn't cover" is usually ludicrous.
    – vonbrand
    Commented Jul 12, 2018 at 12:17
  • You mean "they allow questions"? Most of the time yes, but sometimes no (nor not giving good answers).
    – Udank
    Commented Jul 12, 2018 at 12:17
  • @Udank No, I meant "And if the lecturer's quality of teaching is so low that they really just recite the book without adding anything, I don't think the problem is the structure of the lecture, it's their motivation, skills, or time constraints."
    – JiK
    Commented Jul 12, 2018 at 12:20

Because most students don't read the book, and in many cases can't read the book. Exact statistics vary somewhat by type of institution, of course.

  • In 2016, 28.1% of students at 2-year institutions, and 10.8% at 4-year institutions, required remedial English/reading courses (link, p. 15, Table 1).
  • As a more restricted example, at CUNY in 1997 61% of students at 2-year institutions, and 43% at 4-year institutions, failed entry reading exams and were placed in remedial courses (link, p. 51, Table 3). N.B.: Within the last year CUNY terminated testing and remediation in reading.
  • Books being read in high school now have an average 5th-grade reading level (link).
  • Books such as Help! My college Students Can't Read by Amelia Gamel are now somewhat in demand (link).

The trend of the so-called the "flipped classroom" does something like what the OP suggests; learn basics before class, and exercises further in the class -- of course, to my thinking, this is just "traditional classroom". Although the current trend expects watching video lectures, not reading, which bewilders me when high-quality textbooks are available. Anecdotally, from practitioners I've been told that they're hoping for a "critical mass" of students to do advance prep work before class and engage in discussions, which may at best be counted on one hand for a classroom of 30 students or so.


I have pondered on this a lot and my impression is that: The primary reason is to pace the students, although i really dislike this method. The temptation for student to think that they will read the book later is too high. What most likely happens is the student starts too late and tries to cram the information. So by going through the material teacher is making sure that when and if the student eventually reads the book or a comparable source they are recieving the information a second or third time. This then railroads you into doing things in the same order as the book.

So the purpose really is to span as much time as possible. Drip feeding information is the name of the game so as to give you maximal time to diggest the info. Sure all examinations could be just in the template read this book and take this test. But the teacher is tasked to also carry along weak students.

While reverse classroom is a really good way to do things. It does quite contrary to intuition require a massively better prepared teacher. Also reverse classroom setups can fail to work for some semesters. The big problem of all the methods that rely on students to do the work outside of classrooms (that dont directly go into graded exercises) is that students have other time pressures. So you better reserve classroom time for students doing their own stuff.

So at the end of the day the talking head lecture is just the easy way out for the teacher! It sortof works, has been shown to work for a thousand or so years. It minimizes the effor, show that its not just the teachers oppinion. And last but not least, it is not different from what others are doing so you will hardly be blamed for doing it this way.

It is also somewhat easier on the student as there is a comprehensive material to fall back on. If the material presented does not follow a book than it becomes really hard for students to cope with any things they didnt understand.


I'm going to answer this based upon my own experiences from collegiate level STEM: Some books are terrible.

Personally, I am a very visual and dynamic learner, meaning I learn best by seeing and doing something.

The most relevant example I can think of was when I was learning fluid mechanics and the followup course, hydraulics, they both used the same book. Almost all of the problems presented in the book are simply word problems, there are no pictures, and are written in such a manner that sort of assumes you have a solid understanding of everything they're talking about. The book is literally 250 pages of text with maybe 30 pictures in the whole thing.

This sucks for me. I can't focus on that well enough to learn it.

Whenever I would work my homework, I would try to draw something to illustrate to myself what the book was trying to convey. It was extremely time consuming and a lot of times, I wasn't completely correct (and thus am pretty much 100% wrong).

Because of this, I focused heavily upon attendance at lectures so that I could ask questions and force the professor to draw out their ideas. In doing so, I understood it better and I'm sure some of my classmates did as well.

In professional practice, I also make people draw things since that is so much more efficient for me than a lot of words.

In addition, I can also exemplify were we to do what you proposed, because that is what occurred with my Freshman chemistry classes. We had a lecture, we had homework from a chemistry book that relied upon reading the book and covered material not related to the lecture, and we had additional online homework that was related to additional material. On paper, Chemistry had only 1 lecture and 1 recitation period like my other classes, but it took up at least 25% more of my very limited time. I found that spreading myself so thin on so many subjects just meant I didn't learn any of them particularly well.

One last thing regarding the recommendation that 10 minutes be allotted for questions on the reading material. A lot of advanced topics cannot be adequately explained with only 10 minutes. A basic structural analysis for statically determinate structures usually requires 1-2 blackboards worth of algebra equations that aren't necessarily difficult, but very time consuming to demonstrate properly. The most useful thing from that class was the demonstration of how critical it was to be diligent at every step of a very long series of equations and it was far better demonstrated in the lecture than the book.


Because not everyone is exactly like you and not everyone learns by reading. https://en.wikipedia.org/wiki/Learning_styles

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    From your link: "Many educational psychologists have shown that there is little evidence for the efficacy of most learning style models, and furthermore, that the models often rest on dubious theoretical grounds. According to professor of education Steven Stahl, there has been an 'utter failure to find that assessing children's learning styles and matching to instructional methods has any effect on their learning.'" Commented Jul 12, 2018 at 19:13

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