That's a good observation, but you can look at this chart from the same source.

It's divided into "total" and "current" expenditures, which are defined in a footnote:

^Beginning in 1980-81, state administration expenditures are excluded from both "total" and "current" expenditures. Current expenditures include instruction, student support services, food services, and enterprise operations. Total expenditures include current expenditures, capital outlay, and interest on debt.^

I'm assuming that "capital outlay and interest on debt" would be the costs involved in building schools and infrastructure. Note that the growth rate for the two numbers is still about the same, implying that most of the cost increases are not in the "capital outlay" category. The multiplier in costs for current expenses since 1970 is 2.39, for total expenses it's 2.37.

The charts basically show that we built the greatest technological civilization in the world while spending one hell of a lot less on education than we do now. The modern education bureaucracy is a racket. And so far we're just talking about primary education.