An increase in school enrollment in the fall of 2005 that some Brookline officials first considered an oddity has turned into an eight-year surge that has the town’s public schools practically bursting at the seams.

Now, on the heels of expanding two schools and planning to vastly expand a third, Brookline is forming a committee to begin considering whether to add a school, and explore what type of expansion may be needed at the high school.

The projects could necessitate one or more property tax increases, and while town officials are wary of the cost, they don’t see any end in sight to the rise in student population.

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“I think at first we all thought, ‘This is an anomaly,’ ” said Selectwoman Nancy Daly. “I think now we can say, ‘No, it’s not reverting to form.’ ”

Since the 2004-2005 school year, the number of students enrolled in Brookline schools has jumped from 5,779 to 7,217 this school year, an increase of almost 25 percent.

The upswing in enrollment has been bolstered this year with a record class of 666 kindergarten students. By contrast, the average kindergarten class had ranged from 420 to 440 students for more than a decade before Superintendent Bill Lupini was hired in 2004.

In the fall of 2005, Lupini’s first full year on the job, the number of new kindergarten students rose to more than 480. The following year, the kindergarten class was up to about 550 students, and the surge has continued every year since.

“While we consider that the beginning of the growth period,’’ Lupini said of his first years on the job, the latest figures “quite frankly make those groups look small.”

Brookline’s growth spurt bucks the state trend in recent years. Since 2003, enrollment in Massachusetts schools has fallen by 35,000, or 4 percent, with slow population growth contributing to the decline, according to a study released in October by the Pioneer Institute for Public Policy Research’s Center for School Reform.

Ken Ardon, the report’s author and an associate professor of economics at Salem State University, said there hasn’t been any clear pattern on enrollment trends in suburban districts. But, he said, shrinking school enrollment in Massachusetts cities leveled off around 2006 and 2007, and some urban areas are beginning to see increasing numbers.

What has triggered the surge in enrollment in Brookline is still the subject of some speculation. The town’s overall population growth has been modest, going from 57,107 residents in 2000 to 58,732 in 2010, according to US Census Bureau figures.

Alan Morse, chairman of Brookline’s School Committee, said he thinks there has been a significant turnover in the housing market, with many families with young children replacing empty-nesters. Morse said he thinks younger families are moving to town for a variety of reasons, including budget cuts to some neighboring school systems, the strong reputation of Brookline’s schools, and the community’s convenient location for people who work in Boston.

To accommodate the additional students, some Brookline schools have turned common spaces into classrooms. This year Brookline has also completed about $40 million worth of expansions to its Runkle and Heath schools, which have students in  kindergarten through eighth grade.

The district is in early design stages of a projected $90 million expansion to the Devotion School in Coolidge Corner.

In the meantime, Lupini said, the school district may need to use mobile classrooms to accommodate 17 additional classes that will likely be needed within the next two years.

The first large class of kindergarten students has now reached the seventh grade, Lupini said, and its arrival at Brookline High School in two years will require the district to address space needs there as well. The high school’s student population is projected to grow from this year’s figure of roughly 1,770 to 2,500 by the end of the decade, the superintendent said.

Morse said he is working with selectmen to establish a long-term facility and space planning committee that will study what the high school’s expected needs, and explore whether the town needs to add a 10th school.  The committee will also study whether the town will need to seek additional taxes through Proposition 2½ overrides to pay for the schools.

In addition to the extra building space, Morse said, the school district will need to hire teachers and support staff for the additional classrooms.

The school board’s chairman said he is hoping the facility planning committee will begin meeting next month, and he expects it will take six to eight months to consider the options, consult with experts, and hold a public hearing on the issues.

“We’re going to have to show the people what we think the financial implications are,” Morse said. “I think that is a tall order. I think it’s going to take a while.”

Daly, who chaired the Runkle School Renovations Committee, said whether the town will need to ask residents to approve raising their taxes remains to be seen.

“We’re certainly not going to be recommending overrides to people without thoroughly looking through this process and seeing what needs to be done and how we can accomplish it,” the selectwoman said. “The override is always the last resort, but it is something we have to look at.”