It's no secret that we've had a rough fall and winter with natural disasters. Even as we write this, fires burn in Southern California, adding to the previous wildfires in the northern part of the state that burned over 245,000 acres in October.

Hurricanes Irma and Harvey devastated communities across Florida and Texas, while touching communities in Georgia, Alabama, Tennessee, the Carolinas and Louisiana.

The U.S. Virgin Islands and Puerto Rico were devastated by back-to-back hurricanes Irma and Maria.

Amidst the trauma and destruction, school districts across the U.S. have shouldered a heavy burden: trying to help their students catch up after missing days, weeks and even months of class time.

Across nine states, the Virgin Islands and Puerto Rico, at least 9 million students missed some amount of school this fall due to a natural disaster, according to an NPR Ed analysis. The analysis compiled missed days from individual public school districts affected by natural disasters as well as estimates given by state education departments.

In Florida, 2.6 million kids missed at least one full week of school, according to our analysis. Overall, the state's students missed an average of 5.78 days.

About 2 million students in Texas also missed at least one school day. The hardest hit? School districts near Corpus Christi, a coastal city on the Gulf of Mexico. Some students there were out for several weeks.

Elsewhere: Aransas Pass, a Texas district serving about 1,800 students, didn't re-open until Oct. 16; that's 34 days after schools were originally closed. Compare that with Houston, where schools reopened 10 days after Harvey.

In Southern California, many schools near Santa Barbara have been closed for the last two weeks, with plans to reopen after the new year.

And those numbers pale in comparison to Puerto Rico. An estimated 345,000 students on the island were affected by the disaster, missing several weeks of school. Many students have left to live with relatives and attend school in the states, particularly Florida and New York.

In the U.S. Virgin Islands, where roughly 13,000 students missed weeks of classes, most schools are now open, with the exception of a few that have been "condemned" by the islands' education department.

All this lost time, of course, is likely to have an impact on student achievement.

A fairly new metric in education, chronic absence, is defined as missing more than 10 percent of the school year — just two days a month. Lots of research has shown that such students are way more likely to fall behind and, eventually, drop out. Especially for those in early grades, where the emphasis in school is placed on learning to read. After third grade, students are expected to read to learn, but if the foundations aren't there, they can struggle.

Under the new federal education law, 36 states plan to use some measure of chronic absence to measure school success.

And while missing school from a disaster is not the same as chronic absence — after all, all the students are absent from school, the hit on learning time is vast.

In the aftermath of these disruptions, some districts are taking creative measures to make up for missed class time. The Manatee County schools in Florida, with almost 49,000 students, added 10 minutes to every school day from Oct. 2 to Dec. 20, along with a shortened Thanksgiving break.

Many districts say they have enough class time built into their calendar that the missed days won't keep them from meeting requirements.

In other places, though, the time lost is just too much to make up. In Texas and Florida, state education commissioners have waived several required days due to the extreme nature of the disasters.

In Texas, those lost days — or weeks — have worried educators in several districts, who are asking the state to delay testing dates or suspend testing requirements altogether.

As it stands, Texas' fifth- and eighth-graders, as well as high school students, must pass state tests to advance to the next grade or graduate.

Most superintendents of districts affected by Harvey say they do not want to delay state tests in the spring, but they're worried that the state will evaluate their districts harshly due to low test scores.

"We don't mind taking the exams, but we don't want to be ... publicly humiliated over something we had no control over," Joseph Patek III, superintendent of the hard-hit Aransas County school district, said during a state legislature meeting on Nov. 14.

Districts across the country could be grappling with this same spring testing issue, when missed class time catches up with students and teachers still dealing with the trauma wrought by natural disasters.

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