The school has shifted the fifth-graders into other spaces in the main school building.
An indoor air study was conducted last month by an independent research company after a problem with portables at Mount Airy Middle School last fall prompted a countywide inspection of that type of classroom. The study detected "elevated levels" of carbon dioxide and fungus in the four Hampstead portable classrooms, according to results released to school officials March 31.
The two probable sources of the fungus are carpeting and the ventilation system, according to the report.
To remedy the situation, the county will clean the carpet and examine the heating and air-conditioning systems to ensure there is adequate intake of outside air. When the school closes for the summer, maintenance workers will probably replace the carpet with some type of tile, officials said.