As a graduate student, i've had to substitute teach a number of times for a variety of classes. I'm wondering if it is really worth while to add this information into my CV. Obviously, it won't hold as much weight as teaching a full class. But if it is worth mentioning on the CV, what category should I add it to? Teaching? Volunteer Service? Something else?
I am going to disagree with Peter Jansson here.
If you mean you stepped in to cover a couple of classes here and there when the regular instructor was sick or out of town, I would say this by itself doesn't constitute a meaningful amount of teaching experience for professional purposes, and shouldn't be listed on a CV. It may have been valuable to you, but I think it would look kind of silly on a CV.
If you were assigned as a teaching assistant for the course, you probably have a line where you describe your responsibilities in that role (grading exams, holding office hours, etc), and you could add "occasional lectures" to that line.
If you filled in for an instructor for a longer period of time, then you could consider listing it ("taught 3 weeks of Calculus 4").
Definitely. Teaching experience is always worth adding to the cv because it reflects that you have gained experience in presentation techniques beyond the usual scientific presentations. The difference to research presentations lies in that the latter involves explaining matters and making material understandable at a more basic level. On its own, such experiences may not be enough so document your teaching experience such as levels of the courses, number of students and amount of teaching. you should also gather evaluations of your efforts. I could add links on teaching portfolios here but a simple search on "teaching portfolio" will give you quite a lot of examples and your own university might also have links worth loking at.
I agree with Peter Jasson. It's worth mentioning in your CV unless you already have quite a bit teaching experience. You should put it under "Teaching".
You're a graduate student. Anything meaningful should be listed in the CV. Many years later, you'll find the substitute teaching looks funny when you're a professor. For now, list it unless you already have more than 2 pages long CV.
Here is my personal experience. I put my number of years teaching experience in my resume while in industry. A lot people were interested in that. It's was one of the most frequently asked questions in my industry job interviews I had. One time, I did ask the hiring manager why he was interested to know. He said it shows that I do know how to communicate.