Two: 10 minute time out. Set instrument down (if in last 10 mins of class, pack up) and sit at table in front of room, one page from Five Minute Theory. Parent email/call during conference.
Three: Immediate parent call - I will stop rehearsal, look their number up, and call them on the phone NOW. If my assistant is available, they can continue rehearsal. Explain that steps one and two were taken, and that their child is now subject to campus disciplinary consequences for consistent misbehavior. Write referral.
It almost never gets past Consequence Two.