I make my living supporting Discourse and am a former educator and teacher educator (I was a professor in a college of education). I’m frequently astounded at what–and how much–it is that many companies convince schools to pay for. Best I can tell these folks must spend an insane amount of money marketing, as their products and support are usually not very good.
And speaking of FERPA, I’m further astounded at how often my wife gets “your child <insert FERPA violation about library books, IEPs, suspension, etc>” emails because some institutions hasn’t an email address.
You don’t need multisite, just a means to configure groups and categories, preferably by integration with some existing authentication system–connecting to that is the hard part, especially since many school tech folks are unable or unwilling to help make that happen. Perhaps that’s why you think multisite is the solution–you just give each teacher the power–and responsibility–of managing who their users are. That might still make sense if the school uses, say, Google auth, then the teacher can just approve who joins.
But I digress.
What are those?