[jbay808]

If a city of 1 million people 50 years ago could afford at the time to build a school fit for 1000 students, why couldn't that city afford to upgrade that school to comfortably fit 2000 students today when it has doubled in population density?

You'd need to hire more teachers, yes, but not more teachers per taxpayer...

[pchristensen]

You get hit several times by the same problem:

Land was much more available 50 years ago, cheaper, and less complex to develop (fewer teardowns, existing infrastructure, etc). A school district that has only developed 20 acre greenfield campuses will have to develop new expertise and capabilities to develop a tighter infill school, and it might cost 5x or more for the same capacity.

Decreased housing affordability means that the price of every employee is much higher, so you either stretch them farther or do without. This is fine for high margin industries like tech and finance; low margin industries either pay lower real wages or improve efficiency with systems. Two big industries where those do not apply are health and education, which have (not coincidentally) inflated at a higher rate than real estate. Lots of specialized labor that's not automatable - expensive.

Then, because school districts are of varying quality (real and perceived), and usually assigned by geographic districts, changing ANY boundaries, especially in high demand areas, can have real effects on property values (again, real and perceived). Enough people will vocally object to boundary changes, even if it means a new school, that it's an annoying headwind to any attempt to increase school capacity.

It's a chicken and egg problem. If the the schools are at capacity, you can't responsibly add more housing, but if you're not adding more housing, why would you add school capacity? Schools are possibly the most local of local interests, and it's easier for any given community to shunt the problem elsewhere, especially if their houses are increasing in value while they stall.

[jbay808]

I don't entirely disagree with you, but I don't think that this fully captures it. I'm not talking about a new school, I'm talking about making an existing school bigger. There's no reason that a schoolhouse has to be just two stories.

Replacing a 2-storey school building with a 4-storey school building should not require purchasing new land, so the cost of land shouldn't matter much. (The temporary school closure would be a problem, but not insurmountable - it happens). The boundaries would be unchanged. A 4 storey building might cost somewhat more than twice a 2-storey building, but that should be more than offset by the fact that in addition to the number of taxpayers having doubled, they've also gotten much wealthier over the last several decades, so there's plenty of funds available.

Each teacher would need a cost of living bonus to offset the higher price of the area, but that's equally the case in a high-price low-density neighbourhood as in a high-price high-density neighbourhood. If your 3000 taxpayers can afford to pay 100 teachers enough to live in an expensive low-density neighbourhood, then your 6000 taxpayers can afford to pay 200 teachers enough to live in that same neighbourhood when it has higher density. And if the added density reduces land values, as many complain it will, then it will only get more affordable per-teacher than it is now.