My high school administrators approached underage drinking like a secret police force.
There were skilled interrogators, effective emotional manipulation, good-cop-bad-cop routines, physical intimidation, etc. There was an administrative employee built like a tank who would be sent to (very publicly) collect suspects from their classrooms for interrogation.
They made plea bargains (which they sometimes didn't honor) for informing on others.
They performed social engineering attacks to increase their signals intelligence capabilities - give us a look at your Facebook account (or just hand over your password), identify these (pseudonymous) Tumblr URLs, etc. and we won't destroy your future by calling your college and having your admission rescinded.
They made deals and adjusted punishments based on whether or not you would identify photographs.
When there were reports of drinking on one of the international class trips (to a country with a low drinking age) they rounded up and interrogated everyone from all of the foreign trips. A good portion of the senior class confessed and was suspended. Because some people ordered wine with dinner in France.
If a party was busted by the village police, they'd brethalyze and ticket every single person, then notify the school - which would kick them out of their current extracurricular activity for the remainder of the season/play.
I turned 18 and went to college. We were taught about responsible drinking - extensive lessons on consent, standard drink sizing, alcohol poisoning, etc. And we were told that administration and the university police are concerned only with safety and noise. RAs know about parties in the dorms (in fact, they have to be registered and neighbors are given a chance to veto if they have a test the next day or something) and do not care. The university police shut down apartment parties for noise complaints but make no inquiries as to the ages or intoxication of the partygoers.
So, to answer your rhetorical question: that. That is going to happen to them when they turn 18. Authority will stop caring about bullshit.