Changes to the formula the three up-Island towns use to divvy up education costs won’t be up for discussion at annual town meetings this spring.

Selectmen from West Tisbury, Chilmark and Aquinnah met to discuss potential changes to the funding formula last Thursday afternoon in the West Tisbury Library. They agreed a new proposal wouldn’t be ready for this year’s warrant article deadlines, opting instead to hold special town meetings next fall if they decide to make changes to the formula.

Selectmen said any changes would not be adopted until fiscal year 2020 at any rate.

“This doesn’t change the course of where this was going from the beginning, it just means we have a little more time to get there,” said West Tisbury selectman Cynthia Mitchell, who heads the tri-town task force.

Chilmark selectman Warren Doty said in the meantime the up-Island regional school district committee can move forward with budget calculations.

“We assume that the school committee will come up with a good budget and [will be] doing a good job with funding the schools,” he said. “We’re only discussing how we’re dividing the pie.”

The funding method for the two schools has long been the subject of debate, with some taxpayers and elected officials in West Tisbury arguing they are responsible for an unfair portion. The current formula dates to 1994, although there have been some amendments since then. The current task force was formed late last year to discuss alternatives.

The up-Island regional school district includes the West Tisbury School, which includes kindergarten through eighth grade, and the Chilmark School, which includes kindergarten through fifth grade. Altogether, the district enrolls 338 children from the three up-Island towns and 55 children from outside the district.

At Thursday’s meeting, Chilmark finance committee member Rob Hannemann presented some calculations based on what he called the “three-school model,” which breaks the West Tisbury school into an elementary school and a middle school, as had been requested at a previous meeting. His calculations were meant to be a basis for discussion rather than a detailed formula outline.

Mr. Hannemann crunched the numbers for several hypothetical scenarios: what if Chilmark reimburses West Tisbury for some of the difference in per-pupil costs between the towns when West Tisbury students choose to attend the Chilmark School? What if Chilmark pays nothing for the West Tisbury School grades K-5 and vice versa? What if each town pays for each school in proportion to the number of students from that town that attend that school? What if each town just pays a portion of the total budget that corresponds to the number of students from that town in the district?

In three out of the five somewhat complicated scenarios he explored, Chilmark would actually be required to pay less, and West Tisbury would be required to pay more.

“In our discussion as a working group, we felt that more work was appropriate, starting with a notion of a definition — a clear definition — of what the word fair means,” said Mr. Hannemann. “Because what I think might be fair might not be the same as what you think is fair.”

He and others acknowledged the numbers are subject to change as enrollment in each of the schools fluctuates. Mr. Hannemann used enrollment numbers from October 2017 and budget numbers from fiscal year 2019. The upcoming fiscal year budget totals $11.76 million.

The selectmen were briefly sidetracked by a discussion about school choice children from down-Island, for whom the district is paid $5,000 per student, far less than the per-pupil cost of an up-Island student. Some, including Aquinnah town administrator Jeffrey Madison, were concerned about up-Island schools accepting more school choice students from down-Island than they send out.

But school committee chairman Kate DeVane spoke up in defense of school choice money, noting that teachers are already in the classrooms and “the lights were already on” before the extra students switched in. She also made the distinction between school choice money and money used for students with special needs.

“We’ve actually used school choice money specifically to lower the cost of some of the things that we are offering,” Ms. DeVane said.

She noted the differing perspectives between selectmen and school committee members.

“I feel as the chairman of the school committee currently, that the school committee should be much more involved in this conversation because as you guys are looking at these numbers right now, we look at them 365 days a year, and we have some insights that I think are important to making decisions like this.”

The next tri-town meeting to discuss the funding formula will take place after town meeting season, on May 10 at 3 p.m.