Graphs: Money Spend on Education vs Test Scores

Via powerlineblog I came across this graph that was produced by the Cato Institute. Most bloggers are seizing on them as evidence that the public education system is broken and that spending money on education is a futile waste of time, but I think that is a simply a superficial analysis of the situation. There is something more disturbing to these charts than that- the fact that as the amount of money that is spent on education has been increasing test scores have remained flat could mean many different things- that the money being spent on education isn't finding its way to teachers, that the money spent on education has stopped or slowed the stupidity in our nation as parents abandon their responsibility to teach their own children, that the standards and cut scores for tests have been increasing while keeping the scores the same, that the tests themselves are increasingly poor measures of the education that students receive, etc. I don't know what these numbers mean, but I am disturbed by them, and they do suggest that changes need to be made somewhere in the system.