This may have been the unfortunate reality 20 years ago. But security cameras are cheap and ubiquitous. If it's on school property (including school busses), then this should be simple. Separate the kids, review the footage, and punish the kid who started it. The one who didn't start it gets an apology and assurances that they're safe and it won't happen again. The whole "punish them both equally" is insane and sociopathic.