For children, it might seem a gift from above - an unscheduled holiday of sledding and snowball fights, or a chance to sleep in and then laze in front of the TV.
But what parent hasn't spent at least one snow day wondering: Shouldn't that kid be in school?
Now a college professor is launching a study to measure the brain drain that comes when slick roads close schoolhouse doors. When youngsters are sliding down snow-covered hills, their test scores might also be falling, says University of Maryland, Baltimore County public policy professor David Marcotte.
There's a "quite substantial difference" in scores between years when the winters are white and when they are warm, says Marcotte, an economist who studies education.
His hunch is that time lost in the heart of the school year can never really be reclaimed and that schools pay the price in lower scores on all-important standardized tests.
That makes sense to Don Morrison, spokesman for the Harford County school system.
"You want continuity and a routine," he said. "We are kidding ourselves when we say that a day at the end of the school year is as productive as a day in February."
Marcotte is the father of two girls, a kindergartner and a fourth-grader in Baltimore County public schools. He started wondering about the connection between snow days and test scores after seeing how frequently the weather disrupts school.
His preliminary study, which was published in the August issue of the Economics of Education Review, analyzes Maryland test scores over a 12-year period. It shows that the average third-grade math score soared in 1995, a winter with little snow, only to dip a year later when a blizzard blanketed the region. That comes as no surprise to Shawnta Exum, 33, of Parkville, who took her son 9-year-old son, Jahmari, to Towson Town Center yesterday after Baltimore County public schools closed three hours early.
"They do miss a lot of time, and some of their scores and grades will drop when they're not there," Exum said. "When they're not in school, they're not even focused on school - it's out of their minds. They're playing video games, listening to iPods and playing around on their computers. They do nothing even remotely having to do with school."
But Jahmari, a fourth-grader at Halstead Academy of Science and the Arts, chimed in with his own thoughts on the subject.
"I object," he chirped. "I love snow days."
Exum said she didn't so much mind yesterday's early dismissal. After all, it was snowing yesterday, and weather forecasters were predicting a coating of ice and sleet before the wintry precipitation ended.
But last Wednesday, Exum said, "there was no snow in sight, and it did nothing all day. Sometimes they close school unnecessarily, and that does affect their learning."
Kara Calder, a Baltimore County public schools spokeswoman, said that the students' safety must always come first.
"Unfortunately, we can't control the snow," she said, "and at this point we don't have a lot of control over testing dates."
Snowy winters can skew test scores, Marcotte says, because the first tests are administered in mid-March, regardless of school closures in recent weeks. A few makeup days tacked onto the end of the school year don't make a difference.
"It may be that the students learn the same amount at the end of the year," he said, "But the test isn't administered at the end of the year. It's administered on a fixed date in the spring."
In Marcotte's view, his research calls into question not only the validity of the test scores, but also a system that rewards and penalizes schools based on annual tests.
"It really relates to the issue of how we measure progress," he said, noting that the poorly performing schools can see their scores most affected by snow days.
Marcotte and his graduate assistant, Steve Hemelt, were awarded a $34,000 grant last month from the Chicago-based Spencer Foundation to continue their research.
Marcotte suggests pushing back testing dates as one way to minimize the effect of snow days, but he acknowledges that could cause headaches.
It's nearly impossible to change the testing dates, said William Reinhard, a spokesman for the State Department of Education. All of the Maryland School Assessments are administered on the same days to prevent cheating, he said. The dates are set to avoid the peak snow season and religious holidays, and to return results to parents in time for them to make school-enrollment decisions for their children.
In addition, Reinhard said, "We have yet to see any evidence of snow days affecting school performance."
Despite a hearty helping of snow each winter, all of Garrett County's schools are meeting performance benchmarks, said Assistant Superintendent Brenda McCartney.
"Part of it may be that our teachers and students have become acclimated to the snow," she said. "They know that this is how life is for us, and it takes less time to get back to normal."
Still, she wonders, "If we had those additional days prior to the testing, would our scores be even better?"
Carroll County schools Superintendent Charles I. Ecker said that he would support some flexibility on testing dates to account for snow days and other problems.
Although multiple snow days could have an effect, teachers adjust what they're teaching to make sure students get what they need, said Gregory Bricca, director of research and accountability for Carroll schools.
And while flexibility always helps, Bricca said, the curriculum already has "some play and leeway" built in. That extra room is typically designated for reinforcing concepts.
Marcotte said that adding 20 days to the school year also could minimize the effect of snow days.
But when he brings up that idea, he quickly adds: "Don't tell my daughters."
Sun reporters Arin Gencer, Mary Gail Hare, Jennifer McMenamin and John-John Williams IV contributed to this article.