just take the nails away from the kid and contact the parents.
Yes, I agree, but you are ignoring the fact however that citizens are primed to sue schools when they feel the school didn't take proper action with regard to safety. They take the nails away this time. Then the kid does something else where someone gets hurt. All of the sudden, it's the school who gets sued for not taking action early on. It is a lose-lose situation for the school. If they take action, they are slammed for going overboard. If they do nothing, they are sued for failing to take action.