Does he dream/remember his dreams, if so he's oversleeping. If not, could be that he's going to bed on a full stomach, hence his body doesn't need to wake up for food. If he doesn't dream or go to bed full, the best way to wake up is to tea and toast. Loud alarm clocks don't always work for everyone. Also make sure he leaves his curtains open so natural light can switch on his body clock. Heavy sleepers shouldn't be told they need to grow up, the body needs the right stimulus to wake. It's better to have that naturally. Obviously, having a good 7-8 hours is the starting point. Good luck to your gs.