The all-Island school committee and the teachers unions ratified a tentative agreement for a contract that will boost teacher salaries by as much as 11.5 per cent in salary and step wages over the next three years.

The new contract, which goes into effect Sept. 1, calls for a two per cent increase in teacher salaries in the first year, a two and a half per cent increase in the second year, and a three per cent increase in the third year. The overall package also includes step increases, track changes and longevity pay.

Under the new contract, both teachers and students will also add two more days to the school year calendar, and coaches and extracurricular activity advisors will receive a one-time stipend raise.

The yearly per cent increases reflect the added school days, said vice chair of the negotiation committee Dan Cabot. The current school year is 180 days; teachers also work two preparation days and two professional development days. An extra school day will be added in both the second and third year of the contract.

“We are buying extra days in the teachers’ time,” Mr. Cabot said.

Superintendent of schools James H. Weiss said state mandates and an ambitious curriculum have increased the workload for teachers and students.

“Expectations are higher than ever for students, so any additional time we can have with them is a good thing,” said Sandra Joyce, special education teacher at the Edgartown school and co-chair of the teachers’ negotiating team. The two Island teachers associations include the Martha’s Vineyard Educators Association, with teachers from the Edgartown, Oak Bluffs and Tisbury schools, and the Martha’s Vineyard Regional Teachers and Educators Association, with teachers in the high school and up-Island district, as well as support staff from all the schools. The contract applies to the Island’s 268 teachers.

The all-Island school committee ratified the agreement Wednesday night after the teachers’ unions reached a contract agreement on Monday.

In the first year the school districts will spend an estimated $21.6 million in salaries, including step and track changes, and by the third year they will spend an estimated $23.3 million.

The figures are estimates, Mr. Weiss said, because they are based on the current pool of teachers.

“It’s an estimate because it assumes that for the next three years, all the people will still be here and will move from step to step and won’t change their tracks,” Mr. Weiss said. “But that’s not the case. People come and go, we have an estimate based on the people we have now.”

In the system there are 12 steps, each based on years of service, with a new teacher starting at step one.

He said currently more than half of the teachers across the Island are on the top pay step.

“We have a staff that is incredibly seasoned,” said Susan Mercier, chair of the negotiation committee. “That also corresponds to the fact that many of them are at the top step, as well.”

Tracks are based on educational attainment, with salaries varying on degrees received.

Coaches and extracurricular activity advisors have a separate pay scale than teachers, said Ms. Mercier, and will receive a one-time increase of five per cent in the first year.

“When we looked at that salary scale compared to other places, we were a little low,” Ms. Joyce said, noting that the stipend does not increase with every contract.

The committees have been negotiating since October; the last contract in 2010 took 12 months to negotiate, Ms. Mercier said.

“We were in a far different place economically,” Ms. Mercier said. In the first year of the last contract, teachers took a zero per cent increase in salaries. “That’s never easy.”

“This time, there were clear expectations from both sides that we weren’t here to play games,” she said.

“This was a positive and productive negotiation process, and they are not all like that,” said Ms. Joyce who has worked on the past three contract negotiations. “There was very good communication and dialogue between the two teams and that goes a long way in a process like this.”