Let's say a public school has grades K-5 with 2 classrooms of 32 students per grade. That's 12 classrooms, for a total of 384 students. Let's also assume that school gets $6000 per year, per student (total of $2.3 million). The budget is already threadbare, so there aren't many places left to cut.

Now let's say you take away 10% of the students from that school, such that you now have 29 students in each class. The school's budget is now $2 million, but they haven't shed any costs: they still have the same number of teachers, the same buildings to maintain, etc. So they have to get creative with their budget, which is how you end up with crappy local schools that don't have arts classes, a school nurse, or enough books to go around. This causes more students to flee to the charter school system, making the problem worse and creating situations where kids are frequently unsupervised. Worse, these schools are often forced to take on students with no additional funding in the event a charter school goes bankrupt (which happens to 1-2 charter schools a year in most major cities).

I'm sure my take on this issue would be different if I had kids, and the teacher's unions are part of the problem. But we should fix the unions and the schools, not provide an unregulated system where government money is funneled into private businesses with little to no oversight.

I also take issue with your characterization of charter schools as all being run as for-profit corporations. The charter school environment and laws vary from state to state. California as one example has 1,198 charter schools. Only six of them are incorporated as LLCs, the rest are all either non-profit organizations or run by school districts. There certainly are for-profit charter schools, and in some states they have been an issue, but the majority of charter schools are run as non-profits.

Again you are assuming the wrong things about what makes education work IMO.

It's NOT the budget and never have been. My sons school doesn't have anywhere near the budget of a private school. That doesn't mean that they are doing worse.

The entire idea of money being the key indication only make sense if we are talking about litterally not being able to pay for teachers.

You contradict yourself when you then claim that places like Kahn Academy provides similar education for no money at all.

It's way way cheaper budget they run by and they don't have any benefit of having in person teachers.

And yes your take would be different once you have kids for reasons not easily detectable in statistics or public research and you can't set it up in some table and start comparing it purely via non-human metrics.

None the less your characterization of charter schools in general is mostly wrong and that is what I take issue with. Not whether there are problems with some charter schools.