Explanations for the Test-Score Gains

Explanations for the Test-Score Gains
November 1, 2000



After two groups of researchers recently found large test score gains among students who received vouchers in four different U.S. cities, they then looked for explanations.

The randomized field trial research design--which compared similar students who had different treatment--allowed them to eliminate a number of possible explanations for the test-score gains:

  • It was not background, since student and family background were the same for both voucher students and non-voucher students;
  • It was not facilities, since public schools had better facilities than the private schools the voucher students attended;
  • It was not spending, since the public schools spent roughly two times as much per pupil as the private schools;
  • It was not "creaming", or selective admission of the best students, since virtually none of the private schools screened for applicants;
  • It was not expulsions, or getting rid of troublesome students, since no voucher students were expelled or counselled out; and
  • It was not smaller classes, since there was no correlation between class size and achievement.

"Telling African-American families that they should continue to wait for the public schools to address their needs has long ago grown stale," commented the Manhattan Institute's Jay P. Greene, one of the researchers. "These new studies suggest that we shouldn't give African-American students a line; we should given them a choice."