I mean, if you have a class of 20 students (which seems on the smaller end), that would be a "revenue" of over a quarter million per teacher, right? I feel like we should be able to do a pretty good job with that while paying a teacher a decent salary.
That class of twenty needs a building to take place, which in turn needs upkeep. It needs supplies and equipment (workbooks, computers, dodgeballs), and it needs some level of administration[0]. The teachers presumably want benefits too.
At a university, the “overhead” costs of research [1] are on the order of 50%: doing $100k worth of research require another $50k to keep the lights on, the building clean, and the library stocked. A fully-loaded salary with benefits is also about 30-50 percent higher than the take-home amount. Similar math gets you to about $100k, which would be a massive improvement but nowhere near the quarter-mil you might expect.
However, the average also hides the fact that student spending usually isn’t uniform: it’s not the case that each student costs $13k; it might be more like 9k for 19/20 students and a lot more for the one student with special needs (who might require a FTE on their own). This doesn’t scale nearly as well, but it’s important if you want to give everyone a fair shot at success.
[0] The right amount of admin is obviously debatable, but you clearly need some level of management and organization: somebody needs to make class schedules, run payroll, etc.
[1] These rates are negotiated with the federal government, and so theoretically reflect the actual costs pretty well. It’s not obvious how well they translate to a K-12 environment: researchers need more specialized services…but also are a lot less likely to draw on the walls.
I did use the word revenue in scare quotes for a reason - I don't expect that all that money could be given directly to the teacher. On the other hand, the state should be able to achieve quite high economies of scale on administration and purchasing (whether they actually do is something else), and there's no profit to make at the end of the day.
I was actually thinking 50% would make the math easy but probably be a bit unrealistic, but I arrive at about the same place as you I think. Also I'd imagine that most classes are larger than 20, but hopefully smaller than 30.
