Why not just boot the kids acting indecently? There’s no signature or contract needed.
The school just needs to state that lewd or otherwise disruptive behavior will warrant immediate removal from the dance.
Call to parents, come get your moron kid that couldn’t refrain from dry-humping his girlfriend in public.
Case closed.
A much better solution than booting them all out in the streets (after a run to CVS for some Trojans).