A prominent think tank gave Gwinnett County’s school system a D grade for its efforts to provide educational choices, such as access to charter schools, online courses and magnet schools.

The Washington, D.C.-based Brookings Institution’s annual Education Choice and Competition Index gave Gwinnett, the state’s largest school district, high marks for its overall academic performance, but handed out low scores in areas like “degree of choice and fairness in school assignment.”

The index rated Gwinnett 54th out of 112 school districts surveyed nationwide. Gwinnett won the Broad Prize in 2014 for its efforts to close the achievement gap between white and minority students. It offers online courses to some students. Gwinnett’s Online Campus has about 460 students.

Brookings used federal education data, responses from surveys sent to the districts and other research to help compile its findings. Brookings did not discuss the findings with the districts before they were released.