D.B.
One thing I have learnt as a mo,m is that kids, no matter how old, try to see what they can get away with when it comes to us as parents. It is now up to us to let them know from the get go what we accept and what we don't. One sure way that worked for me was "praising around'. They love being praised for doing something good. Ignoring his hitting and throwing things but at the same time, praising his favorite toy for NOT hitting and throwing things worked wonders for me. My son would throw things and refuse to pick it up when told. His favorite toy was a stuffed dog called Percy. I would pick up Percy, ask him to pick the object up, pretend to have him pick it up and praise him endlessly for doing so. My son would then want to pick it up now so he could get the same praise. It's worth a try. In my experience this has worked on more than one child in your son's age bracket. Good luck!!!!