Ever since DS has transferred to the 4yo old class at DC he has been showing aggressive behavior at school. We though initially it was because he transfers early before the rest of his good friends so he was trying to keep up with the older boys but it has continued on and off even when his friends move up. We have seen it ebb and flow on and off over the last 6-8 months. However the last 3 weeks he has aggressive behavior every week. His aggressive behavior includes hitting, kicking, pushing, and tackling. His class is more boys then girls and we don't allow such play at our house but he does it at school at least one or 2 days a week (he goes 3 days a week). A number of months ago we implemented a reward system where if he had 3 days of no aggressive behavior he would earn something like a sleep over with DH, a trip to Dunkin Donuts, a movie night etc. and this system worked more often then not. However the last 3 weeks he has not earned his reward and has been aggressive at school. He also has been struggling at floor hockey where when he is waiting his turn he will hit his friends sticks, or his friends legs/feet with the hockey stick. At home he is great. Just when he is around his peers he seems like he forgets everything. Is aggressive behavior normal at this age (almost 5)? He has never had any issues at school until the move to the 4s. Any suggestions to help?