Let's have a national high school diploma

The main result of "No child left behind" has been schools faking kids' test results and reorienting the curriculum around teaching to the test. How about this instead:

A national high school graduation exam. Take it and you get a national diploma for graduating high school, if your local school says you kept your seat warm enough days to qualify. But the national diploma says what your grade level accomplishment actually was in each major academic area, as a result of that test. So the schools can teach whatever they want, and they can give their own diplomas however they wish, but the national diploma tells colleges and employers what they're actually getting.

It should require that you show an understand of how old the Earth and the universe is and how we evolved from one celled microorganisms over the last 3.7 billion years BTW.