Fordham Institute states the obvious: DESE measures disadvantage schools with many high-needs students. “Achievement measures are strongly correlated with prior achievement — and given that low-income students tend to enter school far behind their peers, high-poverty schools are likely to fare poorly under such measures, no matter how good the school and its teachers are.”
http://baystatebanner.com/news/2017/aug/09/mass-school-evaluations-called-unfair/?page=1