<p>I like 3-4hr classes when I have a larger class or a lab class. When there is lecture or testing I feel I am sometimes loosing them. My college instructors used to call it "Information overload" The brain turns off. Maybe having some guest lecturers or other mobile activities. I always add humor or real life situations and that usually gets them interested in more participation. But truthfully when it is a small class it is hard to keep them going.</p>