So much of what an ideal class size is depends on who the kids are. For my Junior honors class I would much rather have 25 kids than 10 kids (our average class size is about 16). They are motivated and able and the energy and variety of ideas available when there are more rather than fewer kids is wonderful. However I also have an algebra 2 class of kids who have had a history of real trouble with learning in general and with math in particular. There are just 6 in the class. There is time to address each kid's needs. The atmosphere is quiet, supportive and non-competative and the kids learn and are successful. It is an atmosphere that would drive the other kids nuts just as the electricity of the honors class would scare the slower kids to death. I suspect that the more able and homogeneous the group, the more sense larger classes make and it doesn't seem to me that anything I have said should be new or surprising.