My opinion would be, in school the issue would get tied up with the school's in loco parentis status during school hours. But these cops have no such status, and since their actions are clearly in violation of the first amendment according to tons of precedent, they're clearly acting outside their jurisdiction, therefore as common citizens.
I'd be willing to modify my opinion in the face of the opinions of any pro lawyers out here, but this is the conclusion I come to from my reading of law.