Snapping out of a loop means... too much elevator is being used. Tell him to not pull quite so hard and make bigger (prettier) loops.

You take a plane that stall at 30 mph in level flight and stall it at 90 mph by pulling too hard on the elevator. (you'd rip a wing off in most full sacle airplanes doing that...) A model doing a tight loop loses a lot of airspeed and pulls a lot of G force. Right at the top of the loop is the most common place for a plane to snap out if you are pulling too many G's