Voters in West Tisbury will need more than a calculator to sort out the dispute raging up-Island over school costs.

Less than one week after Vineyard schools leaders unveiled financial scenarios showing that it would cost West Tisbury more than $600,000 in one year if it withdrew from the school region, the finance committee is busily crunching numbers and reaching an entirely different conclusion.

The focus rests primarily on breaking up the regional school district and taking the costly Chilmark School out of the equation.

"The most immediate cost savings is for Chilmark to become a town school . . . and for West Tisbury to become a town school," said West Tisbury finance committee Peter Costas. "It would give them the chance to pay for the school they wanted and negate the financial concerns for West Tisbury."

Up in Chilmark this week, a 12-member task force is preparing for its first meeting Tuesday to examine the reasons behind lagging enrollment at their K-5 school.

The debate over the future of the up-Island region comes during a year of increasing financial pressures in the school district, which is made up of Aquinnah, Chilmark and West Tisbury.

Both schools in the district - the Chilmark School and the K-8 West Tisbury School - face declining enrollment and cuts in state educational funding.

The finance committee in West Tisbury believes their taxpayers are carrying an unfair share of the total school costs in the region, and they're backing a proposal at next month's annual town meeting to withdraw from the district.

If a simple majority of voters approves that measure - and the two other towns in the region also support it with town meeting votes - then West Tisbury will break up the school region formed in 1993. If the other two towns don't go along with the vote, then West Tisbury would have to wait six months to vote again and affirm its withdrawal with another town meeting decision.

This week, Mr. Costas said his board is pushing for a move that would separate the Chilmark and West Tisbury schools. "That's one possible path to where we want to go," he said.

Last week, the finance committee turned up the pressure on Chilmark, whose small school enrolls 45 students and posts a per-pupil spending rate of $19,820.

Adding fuel to the finance committee argument were the numbers released in a fifth scenario presented by Vineyard schools superintendent Dr. Kriner Cash: Closing down the Chilmark School and sending its students to West Tisbury would save the school district more than $700,000 in one year.

West Tisbury alone would save more than $400,000 in one year under that scenario. And while it was immediately clear that Chilmark has no intention of closing its school, finance committee members last week latched onto the figures.

Mr. Costas asked, "Are they willing to pay that [money] to keep the Chilmark School open and not balance it on the backs of West Tisbury taxpayers?"

This week, up-Island school committee chairman Kathy Logue questioned not only the cost-savings posited in the Chilmark closure scenario but also the finance committee's interpretation of the numbers.

The assumption made in closing the Chilmark School is that all its students would migrate to West Tisbury, bringing with them reimbursement revenue of $15,000 per student.

"But it's not a given that all of those kids would come to the West Tisbury School," said Ms. Logue. "Given how strongly parents feel about why they are [at the Chilmark School], it's far more likely they go to the charter school or Montessori school."

Ms. Logue then criticized the finance committee. "They've twisted it to say that somehow we're paying a cost they should be paying," she said. "It's not costing us $415,000 to keep that school open."

Still, no one is disputing the cost-cutting sentiment in West Tisbury. "People are concerned about rising costs," said Ms. Logue.

West Tisbury selectman John Early, who has stayed out of the fray in the school cost controversy, said this week, "There have to be some adjustments."

West Tisbury voters will also be looking at a budget override vote this April, asking for more than $117,000 to help fund their share of the up-Island schools.

Selectmen in West Tisbury have no taken no formal position on the article to withdraw from the region, but Mr. Early's two colleagues haven't concealed their views on what they see as cost-sharing inequities.

Selectman Jeffrey (Skipper) Manter has led efforts to question the school spending formula, both in his role as a member of the regional school committee and on the finance committee. Last week, selectman Glenn Hearn also voiced his concerns, telling Chilmark residents that they need to consider picking up a greater portion of school costs.

Up in Chilmark, though, money concerns are not the guiding force. Last week, parents and community members turned out in force to extol the virtues of the family-like atmosphere at their little school, which is set in a new building constructed just a few years ago.

One outcome of last week's meeting was the formation of a 12-member task force, charged with identifying any shortcomings there that could be to blame for low enrollment.

"What is the real reason that people have left the school or chosen not to go to the school?" asked Chilmark executive secretary Tim Carroll. "Is it just convenience? The task force needs to find out those reasons."

The task force, which includes at least two Aquinnah residents, will meet Tuesday at 6 p.m. in the Chilmark Public Library. No school staff members are part of the task force, but they will be consulted as the group meets this spring, said Susan Parker, Chilmark's representative to the Up-Island regional school committee.

Mr. Carroll said the goal is to boost enrollment. Currently, 12 students from Aquinnah and another 14 from Chilmark opt to attend to the K-5 grades in West Tisbury rather than the small school at Beetlebung Corner.

Mr. Carroll believes that voters in Chilmark will stand behind their school. "There are people who would like to close the school and save money, but the majority of them want to have a school in the center of town to preserve the character and community," he said. "They didn't just spend $3 million to shut it down two years later."