My DS2 (age 2y 1m) is a pusher. He started over a year ago with hair pulling and has now moved on to pushing. We go to a music class which he loves, and he is always as good as gold in this class, but in other group situations such as toddler group he can be a nightmare, especially if he is tired. He doesn't mind if the other child is bigger than him, or small and helpless.
When he pushes a child, I say NO, we don't hurt people, and remove him. I also try and pre-empt the pushing by following him very closely and stepping in if I can tell he is about to push. (This is tedious but at least saves me the embarrassment of him hurting someone's child!) More recently I have also been asking him to say sorry (which he does).
Is it now time to introduce the naughty step? I have heard you can do this from 2 years, but to be honest I can't imagine him understanding that he has to sit still for 2 mins! What age did you do it with your DCs, and did you find that it worked??