WHYY By Teachers gather outside Samuel Gompers School in Philadelphia to protest the district's plan to reopen classrooms for 9,000 pre-K to second grade students. (Emma Lee/WHYY) Thirteen city nonprofits that work with children and families released a statement Tuesday calling on the teachers union to abandon its battle with the School District of Philadelphia and allow some teachers to return to their classrooms. The district had asked some teachers to report to school buildings yesterday ahead of a planned return of up to 9,000 young children to their classrooms later this month. The Philadelphia Federation of Teachers has objected, arguing that buildings are not yet safe because of ventilation problems and that members should be vaccinated before returning. Both sides now await a decision from a city-appointed mediator.