The advocacy group Public Interest Law Center says the commonwealth's own data point to the need for at least $3.2 billion in added state funding.
When the state's bipartisan basic education funding commission published its report last year, it came up with a new formula for distributing new state education dollars. The formula acknowledges that districts face added burdens, for instance, when educating students in poverty, or those still learning English.
But the panel very specifically avoided a crucial question: how much money would it take for all students to score proficient on state tests?
So the Public Interest Law Center did its own analysis.
"Nobody has been actually talking about what districts really need," said staff attorney Michael Churchill.
The Law Center's report finds that if the tenets of the new formula are applied to the average instructional costs of schools statewide, a "conservative" estimate shows the need for $16.5 billion dollars in added support — $3.2 billion of which it says should come from the state.
To put that in context, the state spent $5.72 billion in 2014-15 on regular education.
To reach this $3.2 billion figure, The Law Center and other advocates are pushing for a $400 million increase in each of the next eight years.