Curious
Were "physical plant" costs (construction and maintenance of schools) included? Vehicle maintenance and fuel (or the equivalent in contract bus service)? Liability and health insurance? Food service? Security?
"Tripled since 1960" does not surprise me, even if the numbers you looked at were solely books and materials, plus teacher's salaries and benefits. Unfortunately, the fact that teachers' income increased by less than half of all other costs doesn't surprise me, either.