If I'm going to give students the course X in next semester. Should I have full understanding of the subject before I teach them or can I learn about the topics before I go to the class and then teach them?

The idea that I want to reach is it good to study the subject in the same semester or should I study before?

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    Both! :) Seriously! Commented Mar 23, 2017 at 22:59
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    This happened to me when I was an adjunct professor at Princeton. I was asked to teach X, which sounded a lot like something I (a) had already taught and (b) knew a lot about. After agreeing, I learned the previous instances of the class were really 50% X and 50% Y, where I had much less knowledge. I read the entire textbook the summer before the class. I definitely don't recommend learning it just ahead of the students -- hard to create a syllabus, answer questions from someone who looks ahead, etc. Commented Mar 23, 2017 at 23:08
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    " Should I have full understanding of the subject before I teach them" Many courses taught at the university level are sufficiently rich that no one has a full understanding. But: can you learn while teaching? Yes, and that opportunity is one of the major incentives for many (most?) university teachers. Will the course go better if you start with a higher level of knowledge? Yes! Commented Mar 24, 2017 at 0:00
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    Can I learn while teaching? -- As opposed to what? Is it possible to teach without learning?
    – JeffE
    Commented Mar 24, 2017 at 5:55
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    Fake it til you make it... someone had to say it. Commented Mar 24, 2017 at 5:58

10 Answers 10


. . . the first time I was in a statistics course, I was there to teach it. - John Tukey

In my experience, it's definitely better to learn about it beforehand. If you are really pressed for time, then start reading the textbook or course material from the back, because you really need to know the direction in which the course is going before you teach the material.

Too many times, I have done the opposite and tried to learn the subject at the same time as teaching it. This is really fun and certainly helps you to see things from the perspective of the students, but is not ideal from a pedagogical point of view, as you are too likely to be blindsided by something. The same goes for courses which are part of a series. For example, I once taught a linear algebra class and left out determinants because we were running out of time and we didn't "need" them for the exam. Next term, I got an irate email from the instructor of Linear Algebra 2...

The best possible prepartion for teaching the course in X is having taught it before.

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    Beforehand is always better. I had to redo a lecture because of that, last year. At least we had the time to do that. While I managed to keep ahead for most part of the course, near one important conference deadline I let the ball slip. I was afraid of that from the go, I really don't think that's ideal, voiced my concerns, but I had no choice/say in the matter, postdocs don't get that much choice :) Commented Mar 23, 2017 at 23:57

A real scholar is a lifelong student.

But you should know the material that you are teaching sufficiently broad (like you won't be caught ignorant of some relevant factoids) and sufficiently deep (like you won't be caught not understanding some relevant factoid) that your authority of the subject is not questioned and you won't be embarrassed. (And the students will not think they're getting screwed with regard to their tuition dollar.)


TL;DR: You owe your students to familiarize yourself well enough with the subject matter before teaching it.

Should I have full understanding of the subject before I teach them or can I learn about the topics before I go to the class and then teach them?

While it is usually not impossible to teach a subject as you study it yourself, or immediately after you've done so - it is highly inappropriate, ethically, both as an academic, and in terms of pedagogic effectiveness:

  • You are risking passing weaknesses in your understanding after an initial/brief study on to your students.
  • You will not be able to provide your students with the perspective of someone who has dealt with the material in more than one context.
  • You are likely not to be able to answer some of the students' questions about the subject matter.
  • You will likely not be able to plan for getting finer points, ones which are more difficult to understand, over to the students - you will be expending most of your efforts in merely remembering what you've just learned.

et cetera. So - don't slack off.

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    I’ve given courses before where I learned the subject matter at the same time as teaching it. In fact, for TAs I’d say this is not that uncommon. Still, I completely agree with this answer. While it’s possible, it’s bad. Avoid being in such a situation if at all possible. Commented Mar 24, 2017 at 13:03
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    @KonradRudolph: The thing with TAs is, universities don't want to bother paying them to study material they're about to teach which isn't something they're already well-versed in, so they just send them into class. It's a sign of collective weakness on our part (whether we're TAs or Professors) that we don't resist this more. IMHO.
    – einpoklum
    Commented Mar 24, 2017 at 13:18
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    Yes, I 100% agree. It’s a rotten system. Commented Mar 24, 2017 at 13:21
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    +1 I've been in this situation as a student. The instructor could do the lectures okay, but if you asked anything even slightly outside of them, he was useless. It was infuriating, and showed a complete lack of respect to his students. I never took a class with him again.
    – Kat
    Commented Mar 24, 2017 at 18:51
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    @Kat: The sad thing is, these days there might not even be anyone around him to tell him that's wrong - since it happens so often and management has you do it.
    – einpoklum
    Commented Mar 24, 2017 at 18:54

It's possible (barely). When I started adjunct teaching, among the courses I was offered was a networking class, including lab component, of which I had absolutely zero knowledge. I told the dean that, and he said, "Don't worry; you can just stay ahead of the students by a few pages in the book." And I accepted it.

Now, that was pretty terrible/scammy advice from that dean. First of all, I had to make a determination in the first week to switch the book he'd previously picked for the course because it was terrible (way over our students' heads). Also, I was working furiously for hours every day all semester to learn the material and write presentations. I didn't have time for any activities that semester except just teaching.

I wouldn't recommend going directly from reading the book right to class; I was rushing to get as far ahead as I could, and so prep future quizzes, tests, assignments, labs, lectures, etc., in a scaffolded manner, know what was coming in the future for which to lay the groundwork, etc., etc. I can't imagine that I would have succeeded at that if I was simultaneously taking classes myself, expected to work on papers or research, etc.

But I did wind up knowing an incredible amount about networking, pretty much all in one thunderclap three-month period.


I had three experiences as a student with similar situations:

  1. A professor without much subject knowledge teaches an internet programming course while attempting to create an entirely new syllabus. Result: the worst course I've ever suffered through. Absolutely no learning.
  2. A professor with a strong emphasis in language design teaches a language design course in a language they started learning last semester. Result: not a smooth experience, but rewarding.
  3. A TA with some experience teaches a well-worn 300-level course on distributed design. Professor is technically supposed to teach but is only present ~half of the time, so TA ends up doing much of the teaching and was actually a better lecturer (less rambling.) Result: a good course. One of the most informative I had that year.

My conclusion is that it depends on how close your relevant experience is and on whether or not a quality (or at least decent) syllabus is available. Having veteran TA's can greatly help, although that's independently true.

My recommendation is that you should study and prepare aggressively for this course. Try to learn as much as you can in advance and then also make sure to refresh your knowledge before specific lectures and study sessions.

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    This. Teaching is complicated, but intensely human. To OP: do what you can. Commented Mar 25, 2017 at 22:54

Daniel R. Collins's dean advising "you can just stay ahead of the students by a few pages in the book" is clearly an exaggeration, but it has some truth on it.

I must admit that I have taught several courses where if I had been given the final test of the course in my first day teaching, I probably would have failed it. Anyway, those courses were the most challenging but also the most rewarding I've ever taught.

The key point is that - as others have pointed - you must be able to teach properly every lesson when you teach it. That means not making (big) mistakes, addressing the key points and possible blocks of students, and being able to answer clever students'questions that might depart from the syllabus. In summary, your classes must be able to outperform what the students could learn by themselves, that nowadays includes reading the book but also watching classes in Youtube about the same topics. If a lecturer couldn't, there would be no point on having the lecture.

There are a few key factors that allowed me to succeed, and that I think they are prerequisites to try to teach a subject you previously don't know enough:

  • Your own self-teaching on the subject must be able to outperform by several orders of magnitude the self-teaching ability of your students. Even if your students are intelligent and well prepared, usually you can outperform them because you are more mature, have a lot of experience on related subjects and know better how to study complicated subjects. Once a fellow lecturer who had a PhD in mathematics was worried because she had nearly never studied statistics but she had been assigned a basic statistics course for freshmen engineers. My advise to her was that if she took with her the course book while commuting (she commuted by train), she would know the subject before arriving home that evening. I think she did and the course went very well.
  • The course syllabus and material should be prepared beforehand by anybody more knowledgeable. Changing the syllabus or the book or even preparing exercises and slides is way more difficult than teaching lessons. If there is an established path, I strongly recommend to follow it the first time you teach a course unless you are very sure about what you are doing.
  • And last but not least, time. You must be willing to invest a lot of time studying the subject - a lot more than your students do. Of course, that means that if you teach to earn a living, teaching a subject you need to learn is a very inefficient way to invest your time to make money. For me that's not a big problem because being a part time lecturer in my country is such an inefficient way to make money that it can't be noticeably worsened, but other people might see it in a different way.

In summary: It is possible to teach such a course if you can outperform the students learning, if the course has been prepared and if you want to invest a lot of time in it. It's a real challenge, and you will only enjoy it if you are willing to take the challenge; otherwise it could be a real nightmare.

And an end note: I've done this in on-line and off-line courses. In on-line courses it is a bit easier because you don't need to answer difficult students questions in the spot, and you can research the answer for hours if needed.


It's best if you study the materials first, and would be generally expected in contemporary training scenarios, but it's not strictly necessary.

More important is that you be able to spot where students are having trouble with learning the materials, and set them straight.

Just because you know something yourself doesn't mean you can teach it. A lot of expert doctors are not expert teachers; the same is true of expert programmers, mathematicians and other experts.

The skill of a teacher as a teacher is more important than the teacher's skill as a practitioner of the subject taught. The teacher's skill is in identifying the blocks his students encounter in assimilating the subject, and handling them so the student successfully masters the subject.

At the very least you should have some idea of the questions that students are likely to ask and know where they can find the correct answers—even if you don't know all those correct answers at the tip of your tongue.

I teach a class on Git, the popular version control software. Git has options and commands for literally every scenario imaginable, the result of an open-source tool being used by (and improved by!) open source developers for more than a decade. Any given student will never need more than 15% (at most!) of the available options and commands.

When a student asks me a complex and highly specific use case for Git, it is sufficient that I point him in the correct direction: what commands are relevant to his question and what options will help him accomplish his purpose. I don't have to show off my mastery of those advanced options to help him learn them.

Finally, here is a relevant excerpt from one of my favorite Science Fiction novels:

I liked Prof. He would teach anything. Wouldn't matter that he knew nothing about it; if pupil wanted it, he would smile and set a price, locate materials, stay a few lessons ahead. Or barely even if he found it tough—never pretended to know more than he did. Took algebra from him and by time we reached cubics I corrected his probs as often as he did mine—but he charged into each lesson gaily.

I started electronics under him, soon was teaching him. So he stopped charging and we went along together until he dug up an engineer willing to daylight for extra money—whereupon we both paid new teacher and Prof tried to stick with me, thumb-fingered and slow, but happy to be stretching his mind.

—Robert Heinlein, The Moon is a Harsh Mistress


You'll need to learn as much as you can before you start, and then work hard on it during the whole semester.

I've been dumped into new (as in never before taught) subjects at the last minute where nothing beyond the course description existed a few weeks before the first class (as in "Hey, would you mind teaching this? Starts in ... oh, actually 23 days from now. You might want to think about what textbook you use. What do you think about this one? By the way, you have to submit your draft unit guide for review by Thursday." ... how you might possibly organize it so the students can actually obtain the text in time for the class is left as an exercise for the reader).

This sort of thing has happened to me several times over the years. I wasn't completely unfamiliar with the material, but each time there were some substantial sections of the course I didn't really know nearly well enough to teach at the time I was asked if I would teach it.

To teach it well, you'll have to know the material pretty well by the time you cover it in class (and usually a good deal earlier if you're writing assignments/tests/exams) -- in the most recent case, I learned it well enough to identify many of the errors in the text for the students... and there were quite a few mistakes in some chapters.

Expect to work at least 4 to 5 times as hard as the better students do on the parts of the subject you don't know really well (after all, they have someone explaining it to them, and they only have to answer things you have to both figure out to ask and answer, and give ideal solutions for -- that's a whole different level of knowledge).

If you get to teach it a second time, that will go much easier.

  • +1 for "Expect to work at least 4 to 5 times as hard as the better students do on the parts of the subject you don't know really well"
    – Pere
    Commented Mar 4, 2018 at 10:48

After finishing the university, I was offered a teaching job from the education center. The course was web application development. At that time, I didn't have much knowledge in this field, I was still elementary-learner created few websites so far. Then, I said yes without hesitating since it was a good chance improve my knowledge. I used to work hard every time a day before each class. I did well, next year again I got this course and I improved my teaching ability as well. So, it's a good way to improve knowledge on the specific field, however you should enjoy teaching as well. If you don't like teaching, it's difficult.


Having done both I can only recommend learning it before teaching. You don't need to master everything, but you also should be able to answer spontaneous questions about the subject. And if you're borrowing slides from someone else, you really should know what you're doing! Otherwise you might bump into these problems:

  • You don't know where you should give examples instead of rushing through slides and suddenly you've flashed every slide of the course in one lecture. Just because someone writes one slide for every 30 minutes and you're used to showing one slide per 5 minutes.
  • You probably misinterpret something because you're not familiar with the subject.
  • You cannot go deeper into the subject than the few bullets in the slides.
  • You end up reading the bullets aloud, something you should never do.

I always learn new things when I teach, so you really can't master everything beforehand, but that's the fun in it.

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