Eighteen schools in Dorchester and Mattapan could see fewer dollars headed their way in the coming fiscal year as the city switches over to a new funding formula aimed at more accurate, predictable, and equitable budgeting.

The School Committee unanimously approved the new formula, known as “weighted student funding,” in March as part of the Boston Public Schools’ $829.5 million budget for fiscal year 2012. The move to the new formula comes as the system struggles with the rising costs of health care, teacher salaries, and transportation.

Supporters say the formula ties funding to the student, instead of the previous formula, which focused on programs and school facilities. And the head of the teachers’ union, which has frequently clashed with Superintendent Carol Johnson, said he supports the concept of the new formula.

Boston isn’t alone in pursuing the “weighted student funding” formula; Washington D.C., New York City, Philadelphia, and Baltimore, among other cities, have adopted it.

Richard Stutman, head of the Boston Teachers Union, said Johnson received pushback from some of the schools that are losing funding, and in response, $6 million was eventually funneled to some of them to temporarily offset the expected loss. The formula is also continually being tweaked, he noted.

“The six million was arbitrary,” he said. “The tweaking was arbitrary. Next year she’ll have to tweak it again.”

To smooth out some of the drops in funding and allow schools to phase into the new formula over the next two years, “soft landing” funds are being provided to some schools.

The new formula will also be more efficient and predictable for school administrators, BPS officials say. “Principals can figure out exactly, if they know the student population being served, how much a school is getting and why,” said Matt Wilder, a Boston Public Schools spokesman.

As for the efficiencies, Wilder pointed to Jamaica Plain’s English High School as an example. The school was originally constructed to serve a large number of students, and it was still getting funded under the former funding formula at an old student population level, despite a population decrease, he said. Put simply: Some schools were getting more funds than were necessary, and the new formula is aimed at leveling the playing field for all.

The new formula takes into account schools with high percentages of low-income students and students with English language difficulties, and provides them with a higher amount per student. A weight is attached to the grade level of the student. Each school will also receive $200,000 for administrative costs, such as a principal and an administrative assistant.

In Dorchester and Mattapan – neighborhoods with a total of 32 schools – 14 of them will see an increase in funding, on average per pupil, according to a Reporter review of BPS data.

But eighteen schools will see some downward fluctuation in funding on average per pupil. Holmes Elementary on School Street in Dorchester will see a drop to $7,888 on average per pupil, from $8,214 in fiscal year 2011, when the old formula was still in effect. (BPS is providing the school, which is expecting an enrollment of 315 students in fiscal year 2012, with $640 average per pupil in “soft landing” funds.)

Mattahunt Elementary, on Hebron Street in Mattapan, will be seeing an increase in funds, to $7,868 average per pupil from $7,345 in fiscal year 2011. The school has 713 students, and like Holmes Elementary, a high percentage of them are in the free or reduced lunch program (78 percent,) a similar level of special education students (20 percent,) but with more than double the English language learners (26 percent.)

The projected enrollment for the entire school system in fiscal year 2012 includes 56,534 students, with an average of $7,374 following each student.

According to a February 2011 analysis by the watchdog Boston Municipal Research Bureau, “A total of 90 schools, representing 80 percent of students (45,260), will benefit as a result of [weighted student funding, or WSF] by receiving more resources than a 7.4 percent cut, while 28 schools will receive a greater than 7.4 percent reduction. Approximately 62, or 52 percent, of Boston’s schools will have an FY12 budget increase under WSF.”

When the budget was first submitted in February, Superintendent Johnson said, “For the first time we are submitting a budget that is based on what individual students need and deserve. This is a moral and just financial plan because it places kids – not adults or buildings – as our top priority.”

The budget is before the City Council, which is expected to vote on it by the end of June. Information on the BPS numbers, including a breakdown of which schools are getting an increase or decrease in per-pupil spending, can be found at bostonpublicschools.org/budget.