As the temperatures in Newton, Mass. soared into the mid-90s this week, third grade teacher Valerie Kelly tried desperately to keep her students at Lincoln-Eliot Elementary School cool. Kids stretched out on the tile floor to read while administrators delivered water to classrooms, and Kelly and her colleagues were told to discourage any physical activity.

But despite having the blinds drawn and the lights off, the air inside the 1930s-era building, which has only a few window air conditioning units, felt much the same as it did outside.

"The students had sweat pouring down their faces," Kelly said. "They were lethargic. It was not an easy situation, to say the least."

Newton stayed open through the heat wave, but dozens of school districts across the country canceled classes or shortened their days because of heat, wildfires or flooding in the last two weeks. It is a glimpse of the challenge that climate change will pose—and in some cases is already posing—to the American educational system.

Heat was the culprit in closings in New England, Michigan, Ohio, Pennsylvania, Iowa and South Dakota. Districts in California, Hawaii and the Pacific Northwest cancelled classes in late August because of encroaching wildfires. A number of Phoenix schools closed last month because a monsoon-like rain caused flooding and power outages.

"Safety, security and comfort are necessities in order to facilitate learning," said Jason Lembke an architect at the design firm DLR Group who specializes in designing K-12 schools. "Climate change puts all of these at risk."

One of the most pressing concerns, education experts said, is how the country's rapidly aging school infrastructure, two-thirds of which was built in the early to mid 20th century, will stand up to more intense storms, hotter days, floods and escalating wildfires.

Wildfire season in the American west is about two months longer than it was 40 years ago, threatening the air quality and safety of students for longer periods of the academic year.

In Monroe County in South Florida, 65 percent of schools sit on land that would be flooded if sea level rises just one foot. Many others in the state sit just two or three feet above sea level.

Scientists estimate that temperatures in New York City could increase by as much as 8.8 degrees Fahrenheit by the 2080s, with the number of days above 90 degrees jumping from 18 today to 76 by that decade. Roughly one-third of schools in the city currently don't have air conditioning. In Boston, only 30 of the city's 126 public schools are air-conditioned.

"When heat gets bad there is no question that kids don't function too well," said Adam Sobel, director and chief scientist of Columbia University's Initiative on Extreme Weather and Climate. "There are intrinsic physiological limits beyond which people simply can't do much, and more of the world is going to be reaching those more often."

As temperatures climb, the effects are magnified.

"We may not notice much difference between 75 degrees versus 70 degrees, but we notice a big difference between 95 degrees and 90 degrees," said Park Williams, a climate scientist at Columbia University. "As the globe continues warming, oppressively warm temperatures become increasingly possible. As a result, weeks like this will become increasingly common, when schools and other facilities without air conditioning become unusable."

Most school administrators operate with chronically tight budgets, said Tom Scott, executive director of the Massachusetts Association of School Superintendents. This has limited the amount of climate-related retrofitting districts are willing to do—installing air conditioning or flood protection measures, for example—especially when more immediate structural improvements are needed, like fixing leaky roofs.

"There are a lot people who are noticing that the extremes seem more extreme," said Scott. "People are starting to say we need to act, that we aren't ready for these impacts. But the fact is we're still talking about things that could happen 5, 10, 15 years from now. So there's a limit to this action, it can take a backdoor, when more pressing concerns come up."

Extreme Weather Growing Common

In the three and a half years since Tom Scarice took over as superintendent of schools in Madison, Conn., his district has dealt with Superstorm Sandy and record-breaking cold snaps and snow last January and February. This week, a string of 90-plus degree days forced the early closure of the town's elementary schools, which don't have air conditioning. Scarice said he only remembers that happening once or twice in his 20-year career as an educator.

"We typically average three to five days for snow days each year," Scarice said. "But the last few years that's doubled, with eight or nine cancelled days. The temperatures this week were just too dangerous for our young students."

As climate change increases the severity and frequency of extreme weather, school administrators are increasingly being forced to balance kids' safety with ensuring the school year meets the minimum required days, on average 180 days per year.

"It may be that as the climate changes, and if the changes persist, some districts may remove snow days while others add "snow" and "heat" days to accommodate these changes in weather patterns," said Harris Cooper, an education policy expert at Duke University. Schools could also choose to start their years before Labor Day or shorten mid-year vacations to make up for the delays or closures. "This is definitely something people will have to consider more and more as our climate continues to change," said Harris.

Lembke of the architectural firm DLR Group said when designing a new school building, he and his colleagues look at the climate change risks specific to the area. In Joplin, Mo., which was nearly flattened in 2011 by one of the deadliest and most destructive tornadoes in U.S. history, the architects studied tornado scenarios and incorporated the data to design the new high school and its basement shelter.

Constructing entirely new schools, however, is still rare. New buildings can cost hundreds of millions of dollars. Faced with limited budgets, most U.S. school districts choose to renovate existing structures.

"Climate change is going to mean having to completely restructure our school facilities," said Lisa Hoyos, director of the advocacy organization Climate Parents. "Cities have been writing climate action plans for a while. School districts should probably start writing them too, looking at how climate impacts may affect attendance and what solutions we need to implement."

The challenge, Hoyos said, is ensuring that schools in low-income areas are able to make the same improvements as those in higher-income districts. Also, schools need to make sure they don't exacerbate the problem of climate change. Installing more air conditioning units, for example, should be offset by installing solar panels or increasing energy efficiency to make up for the added electricity demand.

"Climate change impacts are taking place even faster than scientists predicted," Hoyos said. "They are affecting our school systems just like they are every other system. The worst thing would be for these problems to be thought of as random, rare occurrences. But this is the new norm. We have to adapt."