Schools are reducing their reliance on portable classrooms for the 2010-11 year, despite enormous student enrollment.

Montgomery County has 415 temporary classrooms to handle overcrowding, down from 437 in 2009-10. The majority -- 376 -- supplement elementary schools. "That's where we have the biggest crowding issue," spokesman Dana Tofig said.

The "portables" are temporary solutions as the county builds and renovates more facilities, Tofig said. Six new projects were completed for the new school year, including new buildings for Carderock Springs Elementary in Bethesda and Cresthaven Elementary in Silver Spring. Four more schools were renovated, adding classrooms and updates to their auditoriums and gyms.

Montgomery County Public Schools has built 4.5 million square feet of new spaces in the past 11 years. "We'd rather not have students in relocatables," Tofig said.

Although Prince William County will add 15 portable classrooms to 10 schools by its Sept. 7 start date, the district will eliminate 20 from eight other schools for a net cut.

Nine portables will vanish from Triangle Elementary School, which transferred to a new building in January. With a 924-student capacity but 641 student enrollment, the trailers won't return soon.

Schools requiring additional trailers include Battlefield High in Haymarket and Brentsville High in Nokesville, both awaiting the scheduled 2011 opening of Patriot High School to relieve crowding.

Many parents oppose portable classrooms, labeling them insufficient learning environments and potential safety hazards.

"They are not maintained in an appropriate manner. There's mold and mildew that's not controlled, not to mention the safety issues that could arise from kids leaving the portables for a bathroom break in the main school building ... especially at the elementary level," said Elisia George, Montgomery County Council of PTAs parental involvement chairwoman. "This became an issue for me during the sniper shootings a few years ago."

George said she understood that portables were sometimes necessary during construction periods, "if this can be done at a standard that is acceptable, only during permanent construction or renovation of a school building."