PHILADELPHIA — Public schools are usually considered to be safe places for our children. But what if the school buildings, where many kids spend hours of their day, are damaging their health? That’s a question that some Philadelphia parents, teachers and advocates are asking in their fight for better conditions — and more transparency. A series of reports this year from the city’s controller, which inspected 20 of the city’s more than 200 schools, said the buildings were “deplorable and dangerous environment for kids.” What does that look like? Rotting walls, standing water, mold and crumbling ceilings, are just some of the health hazards America Tonight saw through dozens of images obtained from the Philadelphia Federation of Teachers. They offer a behind-the-scenes look at unsanitary and unsafe conditions — from asbestos to toilets clogged beyond repair.

A classroom in Philadelphia's Mitchell Elementary School. Philadelphia Federation of Teachers

Mitchell Elementary School, seen above, is one of almost 150 elementary schools in the city of Philadelphia where the teacher’s union has documented deficiencies – including this picture from September 2015, which shows exposed insulation, plastic over windows, mold and discoloration.

A reading resource room inside Mitchell Elementary School. Philadelphia Federation of Teachers

Perhaps the most stunning images are pictures of children’s building blocks covered with mouse droppings. This picture was captured by Jerry Roseman, an environmental scientist with the teacher’s union. “It's clearly not acceptable,” said Roseman, who has been inside many of Phliadelphia's public schools and written dozens of assessment reports on behalf of the union. “The deficiencies are egregious and the conditions are urgent and immediate.”

Rodent and critter droppings cover building blocks in one Philadelphia school. Philadelphia Federation of Teachers

In 2013, 12-year-old student LaPorshia Massey died after a prolonged asthma attack inside Philadelphia’s Bryant Elementary. While Massey’s medical condition was pre-existing, Roseman had documented the environmental conditions at Bryant as severely deficient: More than 90 percent of rooms had asthma triggers like damaged and flaking lead paint.

Peeling paint documented inside Bryant Elementary School. Philadelphia Federation of Teachers

Philadelphia controller Alan Butkowitz, the city's top watchdog, credits the school district with correcting some of the issues found in his most recent report. But he says that’s just scratching the surface. The most egregious conditions his team found were toilets with human waste sitting inside, he said.

Bathroom facilities were clogged with waste. Philadelphia City Controller

Our crew was not allowed inside any public schools to inspect conditions ourselves or access to any of the school district's own reports on building conditions and environmental health and safety. We did sit down with Danielle Floyd, director of Capital Programs for the School District of Philadelphia, who cited a multimillion-dollar budget shortfall. "There’s really a big challenge between our outstanding need and our ability to be able to address it,” she said. Since 2001, Philadelphia’s public schools have been under state control. Since then, enrollment has dropped and the district’s budget has been cut. For the more than 150,000 children that attend public school in Philadelphia, that’s meant fewer teachers, larger class sizes and fewer janitors. In a lengthy interview, Floyd told America Tonight that her office is committed to providing kids with a building that is “safe, warm and dry.”

A ceiling with mold in elementary school bathroom. Philadelphia Federation of Teachers

Still, for many children, conditions aren’t getting better fast enough. From book closets to bathrooms, children navigate dirty spaces every day — or, as some families have chosen to do, leave. More coverage of Philadelphia schools: Philadelphia’s dirty school problem

Philadelphia's dirty schools may be making students and teachers sick