35-40 is what I call the “sour spot.” It’s too large for meaningful interaction (takes me half the semester just to know who’s there) and too small to be a true lecture session with associated breakout discussion sections headed by TAs. IMHO undergraduate classes should be seminars (enrollment approx. 15 or fewer), discussion/lecture (max enrollment 25), or strictly lecture with breakout sessions (as large as you like, provided that there are TAs for support). Of course I’m not going to get my wish.