This graph represents MCAS results for grade 10.
The Massachusetts state boundary lines are from the U.S. Census Bureau. MCAS data from Massachusetts Department of Elementary and Secondary Education. I gathered geometry data for schools by running each school name through the Google Maps Geocoding API and checking each result as best I could.
The source — mostly some poorly-named scripts to download, parse, get geography, and aggregate data, along with Coffeescript to do the drawing — is available on Github if you’re interested (but it is not well organized!)