...
Why did the federal study show no significant gains? We believe that the study’s “statistical power” was so weak that the student performance gains in SIG schools “would have had to be unrealistically large for the study to have been able to detect them,” in the words of Brown University researcher Susanna Loeb. Moreover, the sample of about 190 schools was not nationally representative, so the results can’t be generalized to the nation. And the states they reviewed had widely varying processes for awarding and administering the grants, introducing a lot of static that can drown out positive findings.
...