It’s not the first time a study has found that Massachusetts students perform the best in the country. But often those studies do not account for a key metric: demographics.

A report published Monday from the Urban Institute, a D.C.-based think tank, however, found that Massachusetts students achieved highest compared to students in other states, even when outcomes were adjusted for demographics.

Massachusetts scored tops in the nation on the National Assessment of Educational Progress, before the scores were demographically adjusted. But other studies have shown that many outside factors, such as family income, can fundamentally affect how students do in the classroom. As Matthew Chingas, senior fellow and author of the Urban Institute pointed out in his study, Mississippi has double the poverty rate of Massachusetts. Mississippi also performs significantly lower in student performance measures.

In an effort to address those factors and truly measure state education systems, the Urban Institute looked at student-level, adjusted scores, based on federal student demographic data, including race, family structure, income, English proficiency, and resources at home.

“This means that states are judged by how well their students do relative to students with similar characteristics across the country,” Chingas wrote.