I thought the exact same thing, but then I scribbled out an imaginary two-good economy and realized that this is exactly accounted for in Baumol's cost disease (I think). If the price of (technology-neutral) school rises, the prices of (technology-neutral) teachers should rise equally. If the price of school is rising faster than wages, then it's a sign there's something more going on than measurement of dollars. I rather liked Scaevolus's alternative framing above to sidestep the issue of measuring dollars.