How do I add school plays to my application?

I’m a bit confused on how to add my participation in the school plays to my common app. Should I add them to the Activities section? If so, should I just say that I was in the cast of this many plays and crew of this many plays? Should I just add a resume with each play I’ve been involved in?

It’s an activity like any other. You list under actitvities. How much you want to expand depends upon how many different functions you did. All acting or all set design do not warrant a book. Acting plus directing plus lighting will need more space.