The District has made a good-faith effort to implement the 2007 law that placed public schools under mayoral control, but there is no evidence that the change in governance has been a factor in improved standardized test scores, according to the first major independent study of D.C. school reform.

The National Research Council, the research arm of the National Academies, said in its report Friday that it is premature to draw sweeping conclusions about the effectiveness of school reform under the Public Education Reform Amendment Act (PERAA). But the report is likely to reignite a simmering debate about the test-centered culture of D.C. schools and other systems across the country.

Researchers issued a strong caution against using what they called the “modest improvement” in test scores over the past four years as evidence that mayoral control had improved learning in D.C. schools. They said such a conclusion required more rigorous analysis of students’ socioeconomic status, along with a better grasp of the District’s complex and rapidly shifting demographics.

“In the meantime, naive aggregate comparison of test scores among race-ethnic groups in the District should be interpreted critically and cautiously,” the study said.

The study is the first in a series of evaluations required by the school reform law. After months of political squabbling and stalemate over the choice of an evaluator, then-Mayor Adrian M. Fenty and then-D.C. Council Chairman Vincent C. Gray settled on the National Research Council in 2009.

The committee assembled by the research council includes a number of prominent scholars and practitioners, including University of California at Berkeley law school dean Christopher Edley, University of Wisconsin sociologist Robert M. Hauser, former Long Beach and San Diego school superintendent Carl A. Cohn and Jon Fullerton, head of Harvard University’s Center for Education Policy and Research.

The main focus of this initial study is to offer the city suggestions on the best way to approach its evaluation of school reform.