Is being a TA for a Biology class considered a useful thing to have on an app? Is this a common activity, or is this the sort of thing that makes an application stand out?
I was a SI leader for three years. I don't know if it's universally viewed as an incredibly awesome experience, but I think it's an awesome experience just to have. I wasn't asked too much about it directly in my interviews but I would definitely look at it positively as a now-interviewer.
I was told by a doctor on an adcom that teaching experiences like SI, TA, and tutoring are good ways to add "points" to your evaluation by the committee.
I would say there are probably a fair amount of people that do have some sort of tutor/TA activity on their application. A lot of the people I know who applied had it (may be biased because I am a tutor). I am sure it does add some diversity and shows you are willing to help. Not something that guarantees an acceptance letter, but will help your app.
I agree. I think it is look a good thing, but won't stand out, similiar to other campus involvement. I really enjoyed doing though. I TA gen chem and found it really help me understand the topics well. So when it came to MCAT prep, I was able to skip about 90% regardless of the fact I hadn't seen the material in ages.