Yet instead of addressing this funding crisis, Question 2 asks us to further strain neighborhood-school budgets by allowing up to 12 new charter schools per year in the state, a proposal that even long-time charter supporter Boston Mayor Marty Walsh calls “ catastrophic .”

Editor's note: Today, Cognoscenti features opposing points of view on Ballot Question 2 , which, if passed, will raise the cap on new charter schools in the state. A view from the other side of the charter schools debate is here .

Here is how charters drain money from community schools:

For simplicity’s sake, imagine a neighborhood school with 1,000 students and a $15,000,000 budget, or $15,000 per child. Assume that a very conservative one-third of this budget might go to relatively fixed costs for maintenance, debt service, basic administration, custodial staff and other costs that don’t vary significantly with student population. Thus, $5 million goes to fixed costs, $10 million to variable expenses such as instructional costs — $10,000 per child. If 200 students “choice-out” for charter schools and take with them perhaps $13,000 each (factoring in temporary state tuition offsets which this year average just 11 percent of assessed tuition) or $2.6 million, that leaves $12.4 million to run the school. Five million is still needed for fixed costs; $7.4 million is left for instructional needs. Dividing this amount by the 800 remaining students equals $9,250 left for instructional needs and other non-fixed costs, or $750 less per student.

And, since charters educate proportionally fewer special-needs children, district schools shoulder a higher percentage of costs to educate these kids, but with fewer dollars per child available to do so.

Even in once well-funded suburban districts, the loss of revenue hurts. In Amherst Regional School District, 116 secondary students attending neighboring charters take $1.4 million in post-reimbursement funding with them (up $300,000 since last year). In the previous three years alone, the district has cut 37 full-time staff positions, eliminated computer instruction and phys. ed. at the middle school, and is considering closing the middle school to close a looming $2.3 million budget gap. Two world languages are now history.

Forget the argument that charter schools bring more money to district schools. State reimbursements come in only when tuition costs increase and only at the discretion of the Legislature, which must authorize the funds annually. In the last several years, only most of the first year of a six-year reimbursement schedule has been funded, about two-thirds of promised revenue. Gov. Charlie Baker has proposed cutting reimbursements by another 22 percent.

But even if reimbursements were fully funded, the extra money simply allows districts a bit of time to plan for their next cycle of budget cuts. How do you make the math work when five kids -- a fraction of a class -- leaving for a charter school take an average teacher’s salary with them?

The end result? The home district is almost always squeezed. Ask almost any finance-committee, Select-Board or school-committee member across the state.

Question 2's large-donor supporters include the Walmart heirs and other out-of-state billionaires like Michael Bloomberg and Houston hedge-fund manager John Douglas Arnold, various undisclosed-donor “dark money” groups, and venture-capitalist and chair of the Massachusetts Board of Elementary and Secondary Education, Paul Sagan. The dirty little secret they aren’t sharing is that opening more charter schools without significantly increasing funding -- even beyond the $1-plus billion per year current deficit, which would only catch up funding for existing schools — will necessarily mean that many community schools will have to close or survive as thin shadows of their former selves.

Don’t imagine that closures won’t happen. Since 1995, when charters first began to take hold, an average 1,600 U.S. public schools per year have closed. Of course, not all closings are directly due to the growth of charters, but Boston, Detroit, Chicago, New Orleans and other municipalities have all shuttered neighborhood schools as charter schools have expanded. The big-money donors who favor a competitive, privately controlled business model of education simply see local, democratically controlled schools as the necessary and perhaps desirable collateral damage of the move towards increased charterization. As business people, they understand that you can’t support hundreds of new schools on the same dime — with their collective additional millions in fixed overhead costs — without shuttering some schools along the way.