Rhubroma: I have to give Scott credit that his graph provided increases in absolute $ as well as %.
About voucher school programs:
You'll probably see some posts here with examples where the voucher program 'works'. And I agree with the data that when you put a few charter schools in bad school districts it 'works'. Why do these schools see good results? First, you get a self-selected group of parents who do give a damn about the education of their children. Second, there is an admission process which can be further selective.
Once you have a select group of students, result will always be better. If you take any public school and only count the results of the upper 50% of the students, of course it does look better.
The problems would come when you put every student in the same system and count them all.
Here's the main reason why US schools are lacking: poor school districts. Money for schools should be averaged out at least statewide, if not nationwide. Second problem: teachers need to be better prepared. Finland, the country with the best school system in the Western World requires their teachers to have a MSc degree in their field. A math teacher who cannot integrate and differentiate himself, cannot teach it to the students. And of course, in order to attract people with MSc degrees to childhood education, the salary has to be consummate.
The voucher program clouds this issue behind a smokescreen of 'free choice' which for a large part of the proponents means introduction of 'creation science' or abstinence eduction. A lot of them do NOT care about bettering the school system as long as religion is allowed to enter the curriculum.
I am scared when I compare school curricula across the world. Good math education does not require much more than a chalkboard and paper/pencil on the part of the student. Even a significant fraction of third world nations provides a more stringent math curriculum in their high schools than the US. Now, of course, high school is unattainable for a lot of their citizens, but that doesn't have to stay that way for long. Just as at one point, we required everybody to learn to read and write, we are at a point where we might have to require everybody to be able to do analysis and probability calculation. Just as illiteracy is unacceptable nowadays, so might be math illiteracy in the near future.