Re: I don't know how to fix it.
I do. Get the government out of it.
Most teachers barely have the budget to just stand there and talk. They're lucky to have the room and the blackboard, at least in the US.
DC, which according to its politicians has the worst possible funding formulas because it doesn't have a state to supplement its budget, spends almost $30,000/student/year. And they're one of the worst offenders with "teachers can't afford basic supplies for their classrooms." If they can't afford basic supplies on that kind of per pupil spending, something about its governance is badly, badly broken.
Progressive's hate the idea, but voucher's for students are the solution. Not only to funding to the teachers but the one-size-fits all mentality of the public school system. Make it a refundable tax credit, for 12 years your kid can use it for any school you want to send him to. What are now public schools get to compete for the dollars just like the private and charters do now. Some will specialize for smart kids, some will specialize for slow kids, and the bulk will specialize for the rest of the kids.