A generation of reforms–including more school resources and new curricula–has failed to improve urban schools. In Oakland, Calif., near where I live, 20% of high school students drop out. Only a third meet the minimum requirements for entrance to the California state university system. The dropout problem is especially severe among African-American and Latino high school students, who are twice as likely to drop out as other students.

School vouchers are seen as a way to bring market competition into this stagnant sector of the economy. But results from early voucher reforms are mixed, and these programs continue…