You can't train artists that way; you can't train writers that way; you can't train scientists or entrepreneurs or any other field that requires creativity or critical thinking.
And what about the ones who fall through the cracks? The high and low performers who get ignored by proficiency metrics? You are abandoning both the most useful (high performers) and most in need (low performers) students.
Charter schools are, across the board, the worst schools in the country. Only about 15% of student performance can even be linked to the school they attend, but charter schools get to cherry-pick the very best students, and then only manage to achieve mediocre results. They are taking the best and the brightest and turning them into the average.
How about Massachusetts? How about New Jersey? How about Maryland, Vermont, New Hampshire, Connecticut, New York, and Minnesota? They have the best schools in the country; they have the highest per student spending in the country; they are among the most liberal states in the country. The worst schools tend to be the least well funded (exception: Washington, D.C., but again, congress interferes with them) and are overwhelmingly conservative.
"Correlation does not imply causation, but it does nod its head and wink suggestively."