West Tisbury selectmen were surprised to learn this week that their town’s assessment for the up-Island school district may spike by some $300,000 next year due to changing enrollment patterns in the district which serves the three up-Island towns.

“It’s largely driven by the [school] census information on the distribution of students which now has West Tisbury with a greater proportion of the enrollment than it had,” selectman Richard Knabel said at the board’s regular meeting on Wednesday afternoon this week. “In any case, it’s a big hit,” he said.

Yesterday Island schools business administrator Amy Tierney explained the assessments which are based on an annual school census of Island students. The census is done on Oct. 1. Enrollment has gone up in Chilmark, adding to confusion about changing assessments in the district which serves two schools — Chilmark and West Tisbury.

“Some people get the wrong impression since Chilmark is adding a classroom but West Tisbury is paying more,” Ms. Tierney said. “What I had to explain to the school committee is that West Tisbury’s proportion at the Chilmark School is larger than last year and its percentage of students in both towns is larger. We increased those budgets so they will have to pay more.”

West Tisbury’s current total assessment for the up-Island district is $5.56 million. A draft up-Island regional school district budget circulated at a meeting this week has that number jumping to $5.8 million beginning July 1, 2011. According to the draft Chilmark would pay $1.9 million and Aquinnah would pay $563,000 in assessments for the coming fiscal year.

The assessment projections may in fact be higher, since three bargaining units in the school district are still settling contracts. Mr. Knabel said he expects the contracts to account for an additional $50,000.

Aquinnah and Chilmark’s assessments are expected to decline by more than $71,000 and $10,000 respectively this year according to the school district’s draft $8.3 million operating budget. Ms. Tierney said the drops reflect corresponding declines in student enrollment from those towns in the school district. A public hearing on the up-Island school district budget is scheduled for Dec. 13 at the West Tisbury School at 7 p.m.

Also on Wednesday, town administrator Jennifer Rand discussed a letter from the Massachusetts Department of Transportation detailing the state’s interest in delegating maintenance costs for state highways to local towns. In October the state department held a meeting with representatives from each town to discuss the proposal. The plan has received a cool reception from Island towns; this week Ms. Rand underscored her own dim view of the proposal.

“I think that we should write them a letter saying thank you very much but no,” she said. “I don’t believe the town should take on that risk. If their point is that we could get a better deal if we bid for work here versus them bidding the whole state, there’s no reason the state themselves could not do a separate bid for the Island and then use Island contractors. Like I said at the meeting I just think that its a terrible idea. . . It’s just fraught with disaster.”

Ms. Rand said her sentiments are shared by West Tisbury highway superintendent Richard Olsen.

Selectmen also announced the resignation of Nicole Cabot from the parks and recreation committee. Ms. Rand took the opportunity to issue a public appeal for more townspeople to volunteer their time on committees.

“It’s awful, we’re down so many people,” the town administrator said, citing openings on the town conservation commission as well.

“If people want to get involved, now’s the time — there’s room for you.”