It has become increasingly difficult for school districts to properly allocate their dwindling budgets because of legislative demands that have to be adhered to. Special Education is a big one, free or reduced price lunch, more sophisticated and ever changing technology needs, etc.
The biggest problem, as I see it, is that American culture simply doesn't value education. There's no political, economic, or policy solution to that....and nothing will really work until that is solved. I have a son in 1st grade whose homework is to read for 20 minutes a night, for example. My wife and I are teachers so we do it. It's a pain in the ass, but we do it. I overhear conversations with other parents who find even the thought of doing it laughable, but will probably be the first to blame the school system when little Jonny can't read at grade level.
Theres really only so much schools can do without a society that genuinely values educating it's youth. It's not a problem you can throw money at or vote away.