If a ballot question allowing more charter schools in Massachusetts passes in November, which cities and towns would be most affected?

The answer may be Springfield and Boston. Or many major cities. Or 72 districts. Or every community in Massachusetts. It all depends which data you use and how you look at the numbers.

Ask advocates on either side of the issue, and the answer is likely to be: "It's complicated."

The ballot question

When a student attends a charter school, the money to educate that child leaves the public school and goes to the charter school, although the district is reimbursed temporarily. Under a current cap, most school districts cannot spend more than 9 percent of their budgets on charter school tuition. The lowest-performing 10 percent of districts can spend 18 percent.

The amount of money districts can divert to charters limits the number of slots open to students, which limits the overall number of charter schools.

This academic year, there are 78 operating charter schools in the state. As of Oct. 1, 2015, the most recent date for which statistics were available, there were 40,200 students enrolled in charters across the state.

Meanwhile, as this March, there were 32,600 students on waiting lists to attend charter schools in Massachusetts.

Question 2 on the Nov. 8 ballot would let the Department of Elementary and Secondary Education approve 12 new charter schools a year outside the spending cap, as long as enrollment in charter schools does not exceed 1 percent of total school enrollment statewide. The new schools could be anywhere, but priority would go to schools in districts with performance in the bottom 25 percent and where there is parent demand for additional options.

Springfield and Boston

The most immediate impact if the ballot question passes could be in Springfield and Boston.

Under the current cap, the Department of Elementary and Secondary Education can approve only 225 new charter school seats in Boston in the current fiscal year and 543 new seats in Springfield.

But there are applications pending to open or expand charter schools that would exceed those numbers.

Springfield and Boston are both low-performing school districts -- Springfield is second lowest in the state and Boston is 24th. They have the longest charter school waiting lists in the state, with 10,300 students in Boston and 3,900 students in Springfield.

If the ballot question passes, the Department of Elementary and Secondary Education could approve more of the pending applications for charters in these cities.

There are nearly 3,000 charter school seats in Boston and 2,200 in Springfield that have already been approved but not filled. These numbers could include, for example, spots in a high school that plans to open next year, or spots vacated when students drop out.

Proponents of charter school expansion say it will increase choices for students in a city like Springfield.

"What we've seen in Massachusetts and across the country is that urban areas, which have historically had more challenges or fewer good educational options, are really clamoring for more options," said Bill Spirer, founder and head of school at Springfield Prep Charter School. "In a place like Springfield, where waiting lists are long and where there aren't as many good options for families as they clearly want, it would have a huge impact."

Spirer said having charter schools test out reforms can make district schools and charter schools stronger.

But expansion opponents say it will further hurt struggling public schools by diverting money away from them. Denise Hurst, an at-large School Committee member in Springfield, said, "I think it's pretty evident that the effects that it would have on the Springfield public schools would be pretty detrimental."

Springfield public schools are losing $35.4 million this year sending students to charter schools, after accounting for state reimbursements, according to data compiled by opponents of charter school expansion.

Hurst said schools have fixed costs, like building maintenance, that do not decrease when students transfer. District schools also serve higher percentages of students who are learning English or have special needs. According to state statistics, charters schools have been improving in reaching these students.

"I believe that what would essentially happen is we'd have a two-tiered educational system, and it would really be unfair," Hurst said.

Other cities

Looking past this year, it is more tricky to determine which school districts would be most likely to get new charter schools.

Currently, there are eight districts that hit the cap for charter school expansion. These include some large urban areas like Lawrence, Lowell and Fall River, as well as Malden, Franklin, Everett and a couple of tiny districts.

Lawrence, Lowell, Fall River and Everett, which are relatively poor cities, all fall between the 10th and 25th percentile of worst-performing schools. That means they are subject to the 9 percent cap today but would likely be given priority for new charter schools under the ballot question.

Lawrence and Malden have charter school waiting lists of more than 1,000 students, Everett's is around 700, and Lowell and Fall River have waiting lists of around 400.

Other districts are close to hitting the cap. Holyoke, for example, has room for just 218 more students this year -- not enough space to allow a new charter school. Holyoke is one of the state's worst-performing school districts and has a waiting list of around 400. Officials at Holyoke Community Charter School have said they want the cap lifted so they can add a high school.

Greenfield, Chelsea, Cambridge and North Adams are also near the cap.

Dom Slowey, a spokesman for the Massachusetts Charter Public School Association, said most of the 72 districts that rank in the bottom 25 percent are urban.

"Not every big city is currently at the cap. But most of them are either at the cap or within a charter of being capped," Slowey said.

Opponents of charter schools stress that although the ballot question sets priorities, it would allow new charter schools to open anywhere in Massachusetts. A school could also open in a low-performing district but draw regionally, accepting students from higher-performing districts, potentially ones that pay more money per student. The ballot question does not limit the number of new charter schools in any single community. Any of these scenarios creates concerns that more money will leave traditional public schools for charter schools.

"Question 2 is bad for our schools because it will allow charters to be created in any community in the state, with no limit on the amount of money that great schools like Chestnut TAG, where I send my son, could lose," said Eric King of Springfield, in a statement provided by ballot question opponents. Chesnut Accelerated Talented and Gifted Middle School was created as part of an effort to turn around failing public schools in the city.

Supporters of the ballot question point out that the Department of Elementary and Secondary Education would still have to approve every charter application, and board members can consider factors like how many charters are already in a district.