Would anyone know of a video contest for high school kids?
No sorry, best best is to setup a GOOGLE ALERT for something like Film makers competition or Film contest. That might give you a head start on ones that pop up.
Check out this website here; http://productioncrate.com/?_ga=1.260015562.1180294189.1487679672 they will be having contest every month the one for this month is almost up.
Hope this is what you were looking for?
It looks like you're new here. If you want to get involved, click one of these buttons!