Just to amplify polarbear's solid point about piano and solitude... when it comes right down to it, a lot of musical practice is solitary, anyway. And when it comes to band rehearsals, children with aptitude find themselves bored because they're not learning fast enough (my DD10 complains about this... she also complains that the brass and drums are too loud/obnoxious, and she can't hear herself play).
There's something to be said for playing by yourself, and learning one-on-one.
There's often a piano role in the orchestra for the school musical, and vocal music teachers love having an accompanist in the group, so they don't have to try to direct and play at the same time. My group's accompanist had 30 kids at her house the night before tryouts, so solitary she was not.
