Sarah Cureton talks with student Amber Lee as she oversees an Earth science class of more than 30 students at Patriot High School on Nov. 1 in Nokesville, Va. (Jahi Chikwendiu/The Washington Post)

The boom-to-bust cycle that transformed Prince William County during the past decade can be traced in its public schools with a single measure: class size.

Flush with revenues from a runaway housing market a decade ago, the Virginia suburb boasted some of the smallest elementary classes in the region, with an average of 17 students per class, according to annual data compiled by the Washington Area Boards of Education. Middle and high school classes had about 21 students.

Now on the heels of a real estate collapse — which caused local tax revenues to fall amid a broader economic downturn — average elementary classes in Prince William have climbed to 23 students and secondary school classes topped 30, making them the largest in Virginia and in the Washington region.

Washington area school boards, squeezed by growing enrollments and recession-sapped revenues, have frequently adjusted their staffing formulas to balance budgets. Average class sizes in elementary school — where research shows smaller classes have the biggest academic payoff — increased by about one student in Arlington, Fairfax and Loudoun counties, reversing a decades-long trend toward smaller classes.

Nowhere was the impact felt as dramatically as in Prince William, which after successive year-to-year increases is now pressed up against state-required maximums in almost every subject and grade level.

Declining revenue and surging enrollment have caused average class sizes in Prince William County to rise dramatically in the past decade compared to other area school systems.

“We are at a point where we have to do something.” said Kim Simons, a parent blogger from Bristow, who described her son’s classrooms at Marsteller Middle School as “wall-to-wall desks.”

The recession’s impact on class size has varied widely around the country, with significant gains in some districts and minimal impact in many places, said Marguerite Roza, director of the Fiscal Analytics Unit at Georgetown University. Districts with the largest class-size increases are often those struggling to manage rapid enrollment growth, Roza said.

Prince William schools have continued to grow by upward of 2,000 students almost every year as the county’s population surged from 310,000 in 2002 to more than 430,000 in 2012, nearly a 39 percent increase.

Research showing that smaller class sizes are linked to better academic outcomes has driven Virginia and more than two dozen states to limit or reduce class sizes in recent decades. The greatest efforts have been made to limit class size in the early grades, and for students who are poor or members of minority groups, because studies show that smaller classes can make the biggest impact for those students.

Parents and educators often rally around lower class sizes, because they foster more personal interaction and more individualized instruction, particularly as public schools become more diverse and students with varying abilities are put together in the same classroom.

Following those principles, the average number of students in U.S. elementary classes declined from 29 in 1961 to 24 in 1996, the National Education Association reported. There is little evidence that making incremental reductions pays off. The strongest results have been tied to reductions of seven or eight students per class.

A growing number of economists and policymakers argue that with limited dollars, schools should pursue more cost-effective alternatives to hiring more teachers, such as expanding virtual school offerings or paying the most talented teachers more to work with larger groups.

Locally, school boards have tried to concentrate resources in areas where they think the impact will be greatest. Fairfax and Montgomery counties use formulas that shift more teachers to some schools with higher rates of students living in poverty or learning English as a second language. (Fairfax County Superintendent Karen Garza has also suggested raising all class sizes by one student as an option to help close a projected $140 million budget shortfall next year.)

Prince George’s County has put extra funding toward staffing in sixth through ninth grades, where performance has lagged.

And in Prince William, school officials are floating possible scenarios for reducing class size just in high-poverty schools or in certain grade levels, such as kindergarten, or sixth or ninth grade, which are considered pivotal transition years.

Prince William supervisors asked the school board to draft a plan to reverse the upward class-size trajectory during a joint meeting in early October, offering parents and educators some hope that the issue will begin to be addressed in next year’s budget.

But reducing class size poses an intense challenge for school districts, particularly after a prolonged period of cost-cutting. The pricey line item often competes with overdue teacher salary increases and pent-up facilities demands.

Prince William school officials calculate that reducing class size by one student across the board will cost $15 million in personnel alone. Then there’s the problem of space. A one-student reduction in all classes would require an additional 175 classrooms. The district already has more than 200 portable classrooms because of facility shortfalls.

Prince William Board of County Supervisors Chairman Corey A. Stewart (R-At Large) said he hopes to reduce class size, but he cautioned that any changes are likely to be incremental, because shrinking classes would require higher taxes.

School board Chairman Milton C. Johns (At Large) said he also supports smaller class sizes, though he’s not sure whether the larger classes have hurt achievement. Graduation rates, test scores and participation in Advanced Placement and other college-level courses are on the rise in the county, he said.

“All these things are happening while we are still vastly overcrowded in our classrooms,” Johns said.

Teachers have paid a high price for that achievement, said Jim Livingston, president of the Prince William Education Association, which represents educators across the county.

He said demands on teachers have grown exponentially, in terms of paperwork and classroom management, and also in terms of the growing diversity of students.

“It’s not just the numbers of students, but the needs of student that have become far greater,” Livingston said.

Sarah Cureton, an Earth science teacher at Patriot High School in Nokesville, has six classes this year that range in size from 30 to 32 students. They sit in long rows in her classroom, which is in a modular facility behind the main building.

Although crowding is an issue across the county, it’s acute in the western end, where most of the development has been concentrated in recent years.

Patriot, which opened in 2011, is over capacity with more than 2,600 students. Anticipating large numbers, Principal Michael Bishop ordered small, mobile desks for the teachers, to maximize space for students.

After nine years in the county, Cureton said she has learned to adapt to bigger classes. To minimize distractions, she designs seating charts with the most talkative or fidgety students on the corners and organizes lab work that students can do without getting out of their chairs.

She teaches students how to advocate for themselves, so they can get the help they need in a crowd.

She doesn’t want students to feel like “a number,” she said. “When you have classes at this size, you have to work really hard to know them on a personal level.”