To be exact, why does TFA need $907 million?

That is the amount that TFA raised from 2006-2010.

EduShyster has done the numbers and explains it all here.

During that time, TFA groomed some 28,000 teachers.

But more important, it groomed leaders like Kevin Huffman, state commissioner of education in Tennessee, now planning for vouchers; and John White of Louisiana, now implementing vouchers; and Michelle Rhee, now raising millions to give to candidates who support vouchers. That’s what really matters.