phoebepanpan, i think my elder son is a similar type with your son. And he's so powerful. So that I always teach him don't hit/ push others.
He sometimes tells me that he hit someone because that classmate hit him. As same as phoebepanpan, I teach him to tell his teacher immediately when the classmate hit him instead of fight back. Otherwise the mistake will be shift from your classmate to you.