I know this is a late response, but I haven't seen this post until now, and we still have the September school this year to cover. We've had several Z4 roadsters attend lately. So for one that is a good sign. However it really depends how your friend sits in the car, we have what is called the broom stick rule for convertibles and roadsters. Basically sit a broom stick on the top of the windshield to the top of the roll hoop or headrest, then sit in the car with a helmet on, if you clear it by an inch you're good, if not talk to Steve Gailits our Track Chair, (his info is on www.trillium-bmwclub.ca
) to see if it will be allowed.
BMW 325I E30 Chumpcar Race Car
BMW 540iT M-Sport (New Family Hauler)
BMW 428i Maranello BMW company car