YA horror, arts school, channeling dead artists

I read this book back in the 80s as a middle-schooler, so my memory may be fuzzy; but here goes!

This YA novel had young teenagers attending a boarding school for gifted students in the arts. (If I recall correctly, the school was in an aging mansion, somewhat far from the nearest town.) The students started producing more and more advanced works of art, but eventually it was discovered that they were being used as vessels to channel the spirits of dead artists. One student (the protagonist? her friend?) was being possessed by the composer Robert Schumann, who was violently insane.

This is about all I remember off the top of my head. I'm curious to know if anyone else recognizes this book -- thanks!

Down a Dark Hall by Lois Duncan.

That was quick.

:-)

Thanks for the help!