The majority of U.S. public school districts need to make major building repairs in at least half of their schools, yet many districts are unable to pay for updates or have postponed them to improve security in case of a shooting, according to a federal report.

The U.S. Government Accountability Office on Thursday released a study that was the agency's first on the issue since 1996.

Based on a survey of hundreds of districts, the report found that many are left on their own to pay for building repairs but often lack the necessary dollars, leaving them stuck with aging buildings that can pose health and safety risks.

At one Michigan school visited by the agency, an engineer has to stay on site to make sure the boiler, which dates to the 1920s, doesn't build up pressure and explode, the report said. A school in Rhode Island said parts of its ventilation system are nearly 100 years old.

The report found stark disparities based on wealth. Districts in poorer areas spend $300 less per student on capital costs than do wealthier districts. Schools in more affluent areas can often call on local taxpayers to add money for building updates, the study found, while schools in poorer areas are more likely to rely on limited state funding.

Congress called for the study in 2019 legislation, but it's being released as Democrats revive a push for new federal money to improve schools. A bill proposed by Democrats last year calls for $100 billion to help repair aging schools.

Rep. Bobby Scott, D-Va., chairman of the House Education and Labor Committee, said the report provides “clear, irrefutable evidence” that Congress needs to act quickly.

“Even before the COVID-19 pandemic, outdated and hazardous school buildings were undermining the quality of public education and putting students and educators at risk," Scott said. “Now, the pandemic is exacerbating the consequences of our failure to make necessary investments in school infrastructure.”

Responding to the report, the Education Department issued a statement saying that “school building infrastructure is and must continue to be handled at the state and local levels.”

The study found that 54% of U.S. districts need to update or replace multiple building systems in at least half of their schools. The most common problems reported by schools dealt with their heating, ventilation and cooling systems. The study found that an estimated 41% of districts nationally need to update or replace those systems in at least half of their schools.

At about half of the schools visited by the agency, officials reported problems with older ventilation systems that leak and damage floors and ceiling tiles.

"If not addressed, such problems can lead to indoor air quality problems and mold, and in some cases caused schools to adjust schedules temporarily,” the report said.

About one-quarter of districts said they need to repair or replace interior lighting fixtures in at least half of their schools, and similar shares said they need repairs to roofing, security, plumbing or windows in most of their schools.

Despite those needs, districts reported that security has become their main priority. Several schools that federal officials visited for the study had recently invested in new security improvements even as other systems were failing.

One elementary school in Florida, for example, had installed new cameras even though problems with its ventilation system required required staff to go to the roof every day to adjust the air conditioning. Federal officials noticed buckets placed around the school to collect water leaking through the roof, and the principal told them it often “rained” in her office.

Schools spend tens of billions of dollars on their buildings every year, but funding methods vary by state and by district. The study found that 36 states provide some level of funding for school construction or renovation, while others leave it to districts to generate support through property taxes, bonds or other local sources.

But access to local funding varies widely. In more affluent districts, local funding made up 72% of their overall funding for building costs. In poorer districts, it accounted for just 35% of overall facilities funding, while state funding accounted for 41%.

One district in Michigan told federal officials it was struggling to repay $1.5 billion in debt for facility costs, leaving it unable to get bonds for further repairs. Michigan doesn't provide money for school facilities, the district told officials, so it has been paying for projects using surpluses from staffing vacancies.

The GAO found that 65% of U.S. districts had conducted evaluations of their facilities at least once in the past decade, but an estimated 16% had not. The others didn't know if a review had been performed.