have him skateboard more, that will work up his balance. the scooter doesn't do much for ya.
My parents put me in karate classes when i was his age, i didn't want to go at first but i ended up really liking it and it changed my life.
they teach you how to fall without getting hurt and really boost confidence if the teacher is good. it also builds muscle and flexibility, which are all good things for snowboarding.
get him some wrist guards, elbow/knee pads and a helmet if he doesn't already have them from skating.
Dude, suckin at somethin' is just the first step to bein' sorta good at somethin'