Yes, they should. They might want to look up information on abuse, sexual health or homosexuality in confidence. There are other ways to accomplish preventing

Yes, they should. They might want to look up information on abuse, sexual health or homosexuality in confidence. There are other ways to accomplish preventing children from accessing inappropriate content, namely filtering by domain which is still possible with HTTPS. Google SafeSearch can also be turned on at the DNS level, still allowing HTTPS to be used and privacy to be maintained. The best way to accomplish more granular filtering is to install a custom browser extension that monitors what pages are visited, no machine learning necessary. And if group policy doesn't prevent browser toolbars from being installed, the school has bigger problems.