Benjamin Franklin High School and Science Leadership Academy, which share a campus in Spring Garden, closed earlier this week after issues were identified during recent environmental safety walkthroughs.
The discovery comes in the wake of a $37 million construction project. The project was supposed to be completed in July, but that didn't happen.
During a news conference on Friday afternoon, Superintendent William Hite said students will not be able to return until construction is complete.
In the meantime, students will be relocated to other buildings, all of which will be assigned by October 10, Hite said.
Town hall meetings are also planned for parents of students affected by the closures on Monday. There are about 1,000 students impacted.
Last month, the Philadelphia Federation of Teachers called for an immediate $100 million investment to eliminate lead and asbestos from every school building after they say a longtime teacher at William M. Meredith Elementary, in Queen Village, was diagnosed with mesothelioma, which has been linked to long-term exposure to asbestos.
The teacher has worked in district schools for three decades.
The school district acknowledged they have many older buildings with asbestos and lead-based paint, but add they have comprehensive protocols to assess and monitor conditions to ensure students and staff are safe.
The district couldn't give an exact number on how many of its schools have asbestos or lead, but the majority of their 220 schools are over 70-80 years old.
The district reports they have completed more than 1,600 asbestos remediation projects in the last three years.
Families, media and the public are urged to monitor the district website at www.philasd.org.