More administrative freedom for school principals is orthogonal to vouchers.

I'm all about charter schools in theory, and still am much of the time in practice, but often the way the funding is structured is ridiculous.

Back when I was in local politics, a charter school opened up in our town. For every kid who enrolled, we had to pay the charter school more than we were paying to educate the kid ourselves. AND bus them there, presumably to add insult to injury. So I'm a little suspicious of vouchers and charter schools even though they instinctively sound like good ideas to me.

>where the amount a school gets for having taught a kid depends on test scores at the end

Presumably you'd be making some assessment of value added, which would be hard of scores alone. A school in an area of high illiteracy that manages to improve literacy levels of pupils could arguably have added more value than a school in a high achievement area where achievement levels are pretty constant - moving people from a fail in Maths/English to a pass might impact their lives far more than moving them from a B to an A (or A to A* as they're now called in the UK; grade inflation FTW).

Actually I think you could just do it on absolute test scores, thus making the smart children more valuable. Schools would compete to bring in the best students, not just to fill their classrooms, otherwise there's no particular incentive to offer the best educational programs. The best schools get the best students and get the most money, the worst schools get stuck with the dumbest students.

Could lead to increased stratification. On the other hand, is it worth spending a lot of money to educate a student who is dumb as a doornail anwyay?