It's nice to have a couple of options to choose from. Your son can 1)Ask him to stop. 2)walk away 3) raise your hand and tell. Can he say, "Please stop hitting my desk with your desk.". Maybe you should ask to have his desk moved.
Do they make a fidget widget for that? I know they make worry stones and fidget widgets. Oh yeah. I think I've seen them for grown-ups with desk jobs. Some kind of squishy anger doll that you squeeze it and the eyeballs bulge. K. Probably not appropriate for 1st grade.
Hey, look! I googled and it's a real thing and they really use it in the classroom.
http://www.nytimes.com/2010/02/07/education/07foster.html?pagewanted=all
