K.S.
Hi S., My 3 year old is the same way now. He learned it from daycare the 2 days he goes. (I think) I put him in time out but only until he calms down and promises he won't do it again before I let him up. You have to remain calm also when talking to him. Another thing I have found that works reallywell is when he does throw things, they go direclty in a trash bag. I keep them there for a few months and then maybe bring them out vs going to the store for a new toy. That seems to work and saves money on new toys
Praise when he does something good is very key. Find something he really likes and let him have it or do it when he is good. I use the pool and the park as special treats for my boys being good. Whats funny is my 19 month old is catching on to the rewards and punishment and he is the best baby because he know the consequences.
I hope this helps.
K.