Note that such a scheme would: (a) eliminate the threat that government might get control over private and religious schools through regulation; (b) not discriminate against homeschooling; (c), by paying flat amounts, do most for poor parents, and motivate them the most; and (d), to the extent that it results in the elimination of the inefficient and grossly expensive government schools, save everybody a lot of money.
That would quickly put an end to this "biased test" crap that we've been saddled with...
I like it!