...the median spending on education is $6600 per year per student at the k-12 level. That's plenty of money.
To make it concrete, let's suppose that we want a 18:1 student-teacher ratio, and that a teacher costs $60,000 a year to employ, and that a high school costs $20 million dollars to construct and operate over its lifetime of ten years, and serves one thousand students. So, assuming straight-line depreciation for the facilities, we are spending $2000/year/student for physical plant. At an 18:1 student-teacher ratio, the cost of teaching is $3300/year/student. Together that's $5300/year/student, leaving $1300/year/student for books, teaching materials and extracurricular activities, if you are in a typical school district.
You are probably boggling at this point, because your public school doesn't do half that well -- the teachers aren't paid that much, the student-teacher ratios are worse, and there is nothing like that kind of spending on teaching materials and extracurriculars. The difference you see is exactly the price of mismanagement and bad incentive structures -- and that mismanagement is due to a) sclerotic and overstaffed school district bureacracies, and b) teachers' unions that oppose any sort of competence requirements or merit pay.
Under the current regime, in most school districts it doesn't matter how much money you spend, because it will all get wasted.