Milk goes on your tray

Carter has gotten in a really bad (and annoying) habbit of throwing his cup on the floor when he is finished with it. So, I am really working with him on telling him "your milk goes on your tray" and helping him put it on there. This morning he did it on his own a few times........only to throw it on the floor 5 minutes later. I am going to be consistnt and hopefully the trend will catch on!