Monday was the first day of class for all but the youngest students in the Brandywine Heights Area School District.
The district's elementary school in Topton remained closed Monday because of mold found inside the building, officials said.
"Our initial air quality control test indicated elevated mold counts in some locations on the first floor of the elementary school," the district's new superintendent, Andrew Potteiger, wrote in a letter to parents.
The district has hired a company to re-clean the first floor classrooms and run dehumidifiers and air purifiers, said Potteiger, who took over as superintendent on Aug. 6.
The elementary school will remain closed Tuesday and open for the first day of class Wednesday, pending the outcome of the most recent air quality test.
"We will ensure that the elementary school is safe through the aggressive cleaning and a reevaluation of the air quality prior to opening school on Wednesday," Potteiger said.
All other schools in the district opened as scheduled Monday morning.