In calculating these ratings, GreatSchools analyzed the 2010-2011 Massachusetts Comprehensive Assessment System (MCAS) English language arts, math and science results and the 2010-2011 Massachusetts Comprehensive Assessment System Science and Technology/Engineering (MCAS STE) biology and physics results for the school and compared them to the MCAS/MCAS STE results for all Massachusetts schools with the same grade levels.
If there are no GreatSchools Ratings for a school, the school's test results were either not reported or incomplete. The different student groups are identified by the Massachusetts Department of Education. If there are a small number of students in a particular group in a school, the state doesn't report data for that group.
Keep in mind that when comparing schools using 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.