Charters are contentious in cities. Should they be put to statewide vote?

Famliies came to the Foxborough Regional Charter School’s gymnasium earlier this month to see whether their children got a spot in the school’s lottery. Debee Tlumacki for the Boston Globe/Globe Freelance

When debating the role of charter schools in Massachusetts, remember these two numbers: 41 and 8.

The first is the percentage of pre-kindergartners through ninth-graders in Boston’s school system who are in charter schools or on charter school wait lists. The second, 8 percent, is the much smaller number you get when you look beyond Boston and consider the state as a whole.

Why does this matter? Currently, the state sets a limit on the number of charters — commonly referred to as a cap. Unless legislators reach an elusive compromise, Massachusetts voters will decide whether to lift that state cap and allow for the creation of more charter schools.

Handing this decision to Bay State voters creates an odd kind of mismatch, because charter schools aren’t really an urgent statewide issue.

Though charters play an increasingly important — and contentious — role in Boston and other cities, in towns and suburbs, charter schools are often a minor player and a rather distant concern.

How big a role do charters play?

It depends on where you are. In much of the state, charters are rare beasts. But they’ve become a natural part of the urban environment, particularly in Boston.

Using information from the Department of Elementary and Secondary Education, the Boston Foundation found that there are about 8,600 pre-kindergarten through ninth-grade students in Boston’s charter schools, compared to just over 40,000 in the public schools. That may not sound like much, but it means that charters educate roughly one of every six kids in the BPS-plus-charter system.

Factor in the kids on charter school wait lists, and more than one in three are either attending a charter or entertaining the idea.

At key educational transition points, the numbers get even higher. Among young kids entering pre-kindergarten, fully 50 percent are either in a charter school or on a wait list. At the sixth-grade gateway to middle school, it’s over 60 percent.

Now, it’s important not to put too much weight on these numbers. the Department of Elementary and Secondary Education has been faulted for its wait list data in the past. And while these estimates have been scrubbed to ensure that kids aren’t being counted multiple times when they apply to multiple schools, wait list totals can still overstate demand — because some families apply just to keep their options open. It would be a mistake to conclude that every wait-listed kid is hungry for the charter school experience.

What these stats do show is that you can’t think of charter school as a marginal feature of the Boston school system. A surprisingly large number of families look to Boston’s charter schools to increase the educational options for their kids.

Do charter schools work?

There’s now a fair bit of evidence that well-designed charter schools can outperform their public school counterparts — and that Boston’s charters are among the best in the country.

Comparing charter schools and traditional public schools is tricky business. You can’t just look at the test scores and see who does better, because they serve different kinds of kids. Among other things, charter schools tend to have fewer English language learners, as well as fewer children with serious disabilities.

But even when you correct for these kinds of differences, and compare identical or nearly identical cohorts, the kids in Boston’s charter schools seem to do better on tests and other measures of academic success. As to why this might be, there are as many questions as answers. Is it the extra class time? Or perhaps the commonly used, no-excuses approach to education? And how much depends on the fact that some charters seem to push out disruptive kids — as happened in one prominent New York scandal involving a “got to go” list?

Despite these lingering questions, the research consensus has grown stronger in recent years: Urban charter schools do seem to help students — and it’s the once-struggling students who enjoy the biggest gains.

Will voters choose to allow more charter schools?

It may not come to that. Legislators could still preempt the ballot initiative by passing their own bill to lift the cap on charter schools. One possible approach is for charter skeptics to allow a limited number of new schools, in exchange for stricter rules to ensure greater access for underserved populations.

But there’s a reason the Legislature has been unable to find common ground on this issue in prior years. Opposition to charter school expansion is quite strong in some quarters, and it’s not clear whether a bill allowing more charters can pass the state Senate.

Should the issue end up on the November ballot, supporters and opponents alike have promised big spending to sway voters across the state.

And the result could ultimately hinge on the simple fact that it is a statewide vote. Past polling suggests this really does matter.

For instance, whereas a 2014 poll found that nearly half of statewide voters opposed new charter schools, narrower surveys of Boston parents and residents of gateway cities have shown overwhelming support.

And there’s a perfectly clear reason for this divide between the preferences of Bay State voters and those of urban dwellers. Outside of cities, this ballot fight is less a vital, personal issue and more a kind of philosophical dispute; cap or no cap, there just aren’t a lot of charter schools.

By contrast, in Boston and other charter hubs, lifting the cap could reshape the education landscape.