2) If amount of money spent were actually a factor then why do we show no plausible link between literacy rate [1] and per pupil spending [2] by the government in public schools. This also doesn't account for how homeschoolers and private schoolers tend to do better in standardized testing (and other areas of academics) and yet homeschoolers spend vastly less in comparison to public and private schools (Finding a public source for spending that I am comfortable with is a little hard, so I am basing this on what I know of spending in my local homeschool groups. The test score comparisons are fairly easy to find.).
3) I think to try and simplify it down to simply the amount of money spent is disingenuous to an issue that, honestly, has very little to do with the amount of money spent and more to do with factors like like of parental involvement, politicization of schools by parents, teachers, and administrators, lack of motivation and work ethic in students, and a whole host of other issues.
4) Ultimately, and this is likely a simplification in and of itself, I think the largest factor is more about the willingness of a student to apply themselves and put in the work. A school is one of the few places where the playing field is as equal as it can be and a child/teenager does not need to be the smartest individual in the room in order to do well in school. They really just need to apply themselves. I remember reading some parenting advice many years ago about how it is better to encourage your children to work hard than it is to tell them they are smart as this helps put the value where it belongs, on hard work rather than one's natural abilities of which they have little control over.
[1] https://worldpopulationreview.com/state-rankings/us-literacy...
[2] https://worldpopulationreview.com/state-rankings/per-pupil-s...