Anytime there is a change in behavior something traumatic has happened to your child. The trauma may not be trauma to others but to him it is, and then it could be as traumatic as someone hurt them and they don't know how or if they should tell. Is there a new child, assistant or routine in the class in the last two weeks? Is someone bothering him but when he wrongfully retaliates he is the only one who gets because the other child isn't seen? There are so many scenerios.How does he react when you take him to his class? Does he have friends? Something happened if in the begining everything was fine. Most kids have a difficult time adjusting in the beginning and as time goes on they become better behaved. But he is the opposite. Is he getting his proper amount of sleep that he needs, is he getting breakfast? From years of working with preschoolers, I have seen where hunger and lack of rest can be reasons for misbehaving. But I would ask the teachers those questions about recent changes in the class, and at home consider his breakfast, sleep time and even tv watching and/or if there is anything new in his home life. Is he an only child? Are you able to volunteer a few hours a week( 1-2 here or there) In disciplining him for his behavior be consistent and not hard on his person, but on the behavior; it could be he does not know how to communicate what is wrong. This is a great opportunity to teach him social skills, but delve deeper into what is going on with him on the inside.I have written a book An Essential Practical Guide to Family Living that addresses child rearing and family relationship issues. It can be ordered at www.destroyingyokes.com Also use the travel time to school as time for you to bond. Prepare him for his schoolday by asking questions about the class,singing classroom songs and telling him what you plan for the afternoon when you pick him up, talk about cheerful things, make sure you give him those moments before he goes off to school. This shows your interest in what he does when he is not with you, and you learn what is going on in class, and this lets him know you CARE about everything in his class,not just when he gets in trouble. Males need affirmation and feeling special. If he knows you will ask him about different kids in the class and what he did, he will want to have good things to talk to you about.Tell girlfriends, and other phone buddies you HAVE to spend this time with him, and you will call them when you drop him off. And the ride home is the same thing, NO PHONE.Do what needs to be done now and the later will be so much easier.