Another thing I have heard from another daycare provider I know is to stand right beside the child throughout mealtime and every time the child tries to throw, you grab his hand and say no and make him put it on the tray. I could never follow through with this myself because I have so many little ones who need my attention during mealtimes (I serve small amount to reduce waste, so I am often doling out more to one kid or another etc). However, if you have a smaller group or a less needy group, this could work too.