How large is too large for a class?

If you were to deliver a series of lectures, I don't think it really matters how many would attend. The more the merrier. You wouldn't need to get personal with them anyway. Neither would you need to know their names. Maybe then when question time comes, you will have more questions with more variety too. However, a class you have to handle from beginning of a semester until the end, should not be more than 30 if you want to really teach each student well. Classes of 40 to 50 are just horrible! Imagine handling a writing class of 48! That can kill you. Imagine the pile of papers you have to read and correct! You couldn't even enjoy writing projects with your students. I think the younger your students are the less in number they should be. The young need more attention.

I have done a lot of teaching, both in classroom settings and one-on-one, and I've found that anything over 20 limits the level of reasonable interaction between teacher and student, and anything over 35-40 basically becomes a lecture with no interaction. With a class of around 20, the teacher can expect to have some interaction with most of the students individually (asking questions, calling on people, etc.), but anything over 30 makes this pretty difficult.

When it come to class attendant numbers, I say the fewer the better... Anyone who has ever had to sit for more than a half hour in an over-crowded lecture hall will certainly agree with me... Although today's technologies make it possible to give lectures to 1000 or people at a time, I still don't think it's an appropriate way to teach... or expect anyone to learn... Most students in this situation will bring a recording device, hidden of course, and recored the session while taking a nap! LOL!

For lectures for non-professionals, I believe a class size of 40-45 should be the maximum. For professionals e.g. doctors, business men, etc. a class size of 100 would still be alright. Pros have more motivation and discipline (supposedly) to sit down and listen to a lecture. We know how students are... especially with tough subjects/boring classes. They hardly listen.

I'm a primary teacher, so for me I would find 40 a really struggle. When I was a supply teacher I taught a couple of classes over 35 pupils and found it hard work, not least because I was trying to learn lots of new names. The marking was also a killer - 4 lessons a day with a separate book for each one... Currently my class is 25 - I like it, I have a full time TA, and I feel like most lessons I can give every child the attention they need, there is an opportunity for more intense group or 1 to 1 work with two adults in the room. No child has to wait too long to have their work looked at or their queries answered. I suppose once they get older and a bit more independent you can cope with more of them because there's not so much pastoral care/scraped knees/runny noses and looking over shoulders and ticking books involved - not in a uni lecture theatre anyway I imagine! That said I can happily talk to the whole school (127) in assembly - different to teaching though isn't it - they're listening and taking things in, but I've not got to assess them against the learning objective *is amused at the thought of assessing assembly*