I think some of what Cathy describes is a maturational difference, but I think some of it is the teacher. I would say that DS's K class was better behaved than his First grade class. The reason--Mrs. K was a really good teacher and set up the classroom in a way that worked well for the kids, clear rules, lots of personal attention, lots of opportunities to learn physically, visually, aurally and through interacting with each other. Mrs. 1st, OTOH, was having problems in her home life, was tired and had trouble getting the kids to behave. These were many of the same kids in both classes and their behavior went down hill between K and first.