With school starting in less than two weeks, Montgomery County has firmed up its enrollment forecast: Its student population will surge by 2,864, the largest one-year jump in more than a decade.

Projections call for a record-high student enrollment of 154,153 for the coming school year, said Bruce Crispell, director of long-range planning for Montgomery schools.

The growth continues an upward trend that dates to 2007 and has left school leaders scrambling to add classrooms and relieve school crowding. Montgomery is Maryland’s largest and fastest-growing school system.

“It’s definitely extremely challenging to keep up with all of this growth,” Crispell said, noting that funds for school construction have not kept pace with enrollment. “We’re forever catching up instead of getting ahead of the curve.”

The expected spike, the largest since 2000, could worsen crowding in some places but will be partly offset by new classrooms, including 28 additional portables, a new elementary school in Clarksburg, a rebuilt school in Silver Spring and an addition at a Germantown school.

Community leaders said the enrollment increases will fuel more advocacy for state and county school construction funding.

“It definitely underscores the need we have for more classroom space and somewhere to put all these children, so that we can keep our classrooms to a manageable and effective size,” said Frances Frost, president of Montgomery’s countywide council of PTAs. “We can’t build this quickly with the budget limitations and the construction limitations.”

There is no sign that Montgomery’s enrollment trend will wane anytime soon, Crispell said. This year’s increase, if realized, would mean enrollment has ticked up 16,400 students during the past seven years.

Crispell said his forecast reflects calculations based on trends in birth rates, family migration into Montgomery and more populated grades of younger students aging up through the school system.

The recession that began in late 2007 has been a compounding factor, he said, with many families staying put, as others continue to move into the county. Since 2007, more students have moved from private school to public school than in the past.

Predictions of enrollment are imperfect, but Crispell said Montgomery’s have been in the ballpark, with differences of “much less than 1 percent.”

The best forecast of Crispell’s three-decade career came last school year, he said. He predicted enrollment at 151,283.

It came in at 151,289.

“That’s as close as I have ever been,” he said.