Ok if a child has aggressive behaviour you need much more than a star chart. What does he do at home, is he aggressive towards other children, siblings? If he does, you need to find a suitable reaction that will stop him from laughing. You are the boss, not him. And I really mean this, so should you. Don't shout, take a low and very firm voice, tell him clearly that we never, ever hit. NEVER. We don't push, scratch, hit. NEVER EVER.
Explain to him that if he pushes, kicks, scratches a child it's an immediate red card (football analogy here) and is an immediate punishment, favorite toy goes on the fridge, child has to sit on chair for 4 minutes and has to apologise. If he laughs, take away another toy, tablet, TVs time, game whatever. Whatever works for him. He needs to get it, and you need to be very firm and consistent. He needs to understand that every time he is aggressive something will happen and it will be a punishment, every single time.
A behaviour chart would be helpful if he spends a entire day without any pushing/hurting another child. If he gets five days in a row he gets a reward, a movie, extra playtime.