As he is a small kid, he is doing with out knowing. Once he get to know these things, he will stop doing.
Re: the school, I suggest saying to them that you sought an opinion about his behavior and, while discussing how to handle it at home, the school suggestion arose.
Re: home, I would employ time out (vs the bedtime intervention). A very reliable resource is Lynn Clark's book SOS Help for Parents (see www.sosprograms.com)
Thank you so much for the response. How do we gently tell his pre-school without overstepping our bounds as parents? Right now he is only in time out for 2-3 minutes if that. When we get news that he has had a bad day where he has done something like hit or pinch we do not put him in time out again but we talk to him and send him to bed right after dinner without being able to read books or play with his toys. If we happen to see him show aggressive behavior (this is rare because he is an only child) we immediately put him into time out. Are there any books that you could recommend that might help us manage this better?
Occasional acts of aggression of this sort are not a signs of emotional distrubance. However, the actions invite an immediate and firm response, not only by you but by the school. Any act of aggression should be met with an immediate time out, after which your son should be made to play by himself for 10-15 minutes before he is allowed to join other children. In addition, he should be required to do something nice (e.g., draw a picture) for the child he hurt.