I've seen a variation of this before. Many years ago when I was a school Band Director we had a jazz festival. Our 2 groups (grades 8-12) were in a session run by the clinician. There was a bass player & piano, I think, maybe drums. He put the Blues scales on the blackboard, a scale beginning on the tonic, then ones beginning on the 4th & 5th. He also put several rhythms on the board. The kids took turns soloing. He would point to the scales (usually in I-IV-V order). The kids would use those scale notes and select one of the rhythms. Hey, some of the 8th graders sounded as good as the 12th graders.
I think this is an excellent way to begin to learn improvisation and wish I had been exposed to it in my youth. The only problem was I think the kids sounded TOO good. In that they really were just doing what they were told to do without a real understanding of why. Now, if they took this and really practiced --and listened to a ton of improv recordings-- your on your way.
