> At the same time, school scores started to sag after 2014

That's around the time a bunch of districts in a state I lived in at the time had multi-year teacher pay scale freezes due to budget crunches. Not saying it's necessarily connected to the scores dropping, but still.

Total spending across the country may be high, but it's very much state-by-state and local how much is spent and where it goes. Some states pay teachers pretty well. Some states, the pay really is pretty awful. Some states are OK on staffing levels. Others are in an ongoing staffing catastrophe that's forcing them to cut school days to try to get by.

Meanwhile, school performance is heavily tied to home life and broader community support for students' families. That's why all this effort to improve schools hasn't been as effective as one might hope: the attention needs to go toward much harder problems that have little to do with schools and are really hard to get any progress on in the US. Worker protections, better and less-stressful "safety nets", better policing and a better justice system. That kind of thing. I'd look at least as much at what's been going on with those, and with security and home life for those in the lowest three quintiles of household income, as at schools themselves, to try to find reasons for trends like this.