Burkittsville, Md.

THE latest evaluation of the Milwaukee Parental Choice Program, the oldest and most extensive system of vouchers and charter schools in America, came out last month, and most advocates of school choice were disheartened by the results.

The evaluation by the School Choice Demonstration Project, a national research group that matched more than 3,000 students from the choice program and from regular public schools, found that pupils in the choice program generally had “achievement growth rates that are comparable” to similar Milwaukee public-school students. This is just one of several evaluations of school choice programs that have failed to show major improvements in test scores, but the size and age of the Milwaukee program, combined with the rigor of the study, make these results hard to explain away.

So let’s not try to explain them away. Why not instead finally acknowledge that standardized test scores are a terrible way to decide whether one school is better than another? This is true whether the reform in question is vouchers, charter schools, increased school accountability, smaller class sizes, better pay for all teachers, bonuses for good teachers, firing of bad teachers — measured by changes in test scores, each has failed to live up to its hype.

It should come as no surprise. We’ve known since the landmark Coleman Report of 1966, which was based on a study of more than 570,000 American students, that the measurable differences in schools explain little about differences in test scores. The reason for the perpetual disappointment is simple: Schools control only a small part of what goes into test scores.