The answer, says John LaPlante, is "more than you think." He cites a study from Oklahoma that perhaps as much as spent off-book as on.

So if the official numbers understate the true effort by at least half, where does that the extra money go? Shell games and Enron-like accounting, say the authors. Some money spent on education is funneled through departments outside the Department of Education. Some money is spent (or in some cases, obligated for payment in the future) on the teachers' retirement plan, which has a gross imbalance between promised benefits and income. Some of the money being spent on education now, in other words, is being deferred to the future--a future that will put a tight squeeze on other public priorities and on taxpayers.

The per-pupil amount in Oklahoma could be $11,250 per student, rather than the official number of $6,429. Someone should duplicate this study for Minnesota.