Normally, I'd agree with you, lug-nut, however:
1. School is not private property. Students lockers, etc. are subject to search without warrants.
2. The breathalyzer's only being used at voluntary events. There's no requirement for students to be at dances, trips, etc.
Our school has lost 7 students in the last 4 years due to driving accidents. These kids underage, and they're at events where their actions could impact other kids. If you're stupid enough to drink underage, for God's sake don't go to school events.