Why not fund Americans' educations instead?

Good question! I would love to. I started this when I had very little money as a college student. I could have donated 100% of my money and not made a dent in an American education. With Tanzania I was able to fund a student with so little money, so the leverage was huge.

Eventually I would love to do more work in the US. I'm a postdoc now so I'm still not in a personal position to make a meaningful contribution to an American education, but one day I plan to get there.