Charter school advocates are understandably pleased with some recent news out of New York City. A new study has concluded that charters schools--a controversial innovation in public education--have a more positive effect on student test scores than do traditional public schools. (In fact, the report's authors claim that charters are closing the "Scarsdale-Harlem achievement gap" in math and English, or the divide in test scores between affluent suburban schools and those in the inner city.) Charter advocates are particularly touting how the study reached its conclusion: As The Washington Post puts it, the study meets the "gold-standard" of education research methodology because it was randomized, looking only at students who applied to charter schools through an admissions lottery. The report compares the test scores of students who were accepted to charters via lotteries to the scores of those who didn't get in--and, thus, remained in public schools.