In calculating these ratings, GreatSchools analyzed the 2011-2012 District of Columbia Comprehensive Assessment System (DC-CAS) reading and math results for the school and compared them to the DC-CAS results for all Washington, D.C. schools.
If there are no GreatSchools Ratings for a school, the school's test results were either not reported or incomplete. If there are fewer than 10 students in a particular student group in a school, results are not reported for that group.
Keep in mind that when comparing schools through GreatSchools Ratings, it's important to factor in other information, including the quality of each school's teachers, the school culture, special programs, etc.
GreatSchools Ratings cannot be compared across states, because of differences in the states' standardized testing programs.