I agree with Indigo and Old Dad. Drama. Without them knowing it, getting on stage teaches kids to fail and get up again, fail and get up again. They forget lines (or somebody else does) and the show keeps going. It's really good for kids who might be afraid to fail.

It also teaches kids how to project their voice, keep their bodies still and strong, teamwork, how to share and give focus (and to take it when it is yours to take).