I usually have 10 or less students per class and sometimes find that teaching for a full 4 hour block is like Deborah said "information overload".  I teach in the mornings like some others and I am loaded with energy but not all of my students are so I break the information up so that I lecture for a while then we play some sort of game to try to retain some of the information we just learned or we do some hands on activity to reinforce what was just talked about.  This seems to be working quite well.