Keep in mind that that nastiness was probably caused by 2 or 3 boys egging each other on. That's 2 or 3 (or maybe just one) pupil out of several hundred.

What's the girls' room like? Clean, I bet. That's 50% of the school.

The adults have no excuse for this. When I was in grade school, our teachers ushered us to the restrooms at a stated time every morning and every afternoon. They would have heard the sounds of vandalizing and stopped it.