This winter’s frequent snowstorms have reshuffled lesson plans and testing schedules at schools across the Washington region, and the days off have left students worried about being ready for spring exams. Teachers wonder if first-graders will make their reading goals as they lose ground on snow days, and parents have been surprised by extra homework.

Schools could be grappling for weeks with the academic fallout of one of Washington’s snowiest winters in recent memory, capped by Monday’s late-spring storm and the potential for more this week. Educators say the gaps in instruction time may take an extra toll on students who struggle in class and that college-bound juniors and seniors might face the most pressure because they have lost so much preparation time for end-of-course exams and Advanced Placement tests.

Some county school districts have lost two weeks or more of classroom instruction to snow days: In Montgomery County, for example, teachers might have to extend teaching third-quarter material into the fourth quarter because of 10 full days lost to winter weather.

Fewer school days could mean fewer grading opportunities for students — tests, quizzes, homework — which could affect quarterly grades, teachers said.

Many students will do well anyway, said Joanna Sabatino, a middle school math teacher in Montgomery. But for each class, the 10 days claimed by weather equal “480 minutes of teacher time, and they have to take the same exams at the end of the year.”

Students who struggle have it particularly tough, she said. “The students who desperately need that teacher contact, that teacher check-in, they don’t have the day-to-day interaction,” she said.

In Loudoun County, midterm exams were canceled in January and 14 school days have been lost to snow and ice, the most in the Washington suburbs. Teachers have been coming in early, staying late or working through lunch to help students master material for tests.

“I’ve never seen anything like this,” said Joey Mathews, president of the Loudoun Education Association.

The effects cross all grade levels. More than just creating a scheduling problem for administrators and parents, it’s the children who lose out the most, said Jon Gates, principal of Fairfax County’s Hollin Meadows Elementary School.

“It has to do with momentum,” Gates said, noting that teachers depend on consistency in the classroom to help children learn. Fairfax has had 11 weather-related cancellations this year. “We need momentum, and we benefit from it once we get things moving. Restarting is really difficult.”

Gates said each snow day becomes a double loss: Teachers lose instructional time and then lose additional class time catching up on material students may have forgotten. He said that at schools such as Hollin Meadows, where about one-third of the students are learning the English language, children are especially hard-hit when school isn’t in session.

“Learning English is one of those things where students benefit from being immersed in the language, and that happens more often than not at school,” he said.

Mary Hendley, a reading specialist at Northview Elementary School in Prince George’s County, said she has sent additional reading materials home with her first- and second-graders when there has been a threat of school closings. She has avoided taking sick days, too.

“My goal is to make sure they are reading at grade level at the end of the year,” she said. “When you miss what seems like a month of instruction, it’s a challenge.”

Hendley said teachers with young students find themselves “backpedaling” to review simple routines when students return from snow days.

“It takes [children] a while to remember that they can’t talk when they want, like they do at home, and they can’t get up and walk around when they want,” Hendley said.

Mary Hawkins-Jones, a teacher at Westover Elementary School in Silver Spring, said educators are being urged to continue teaching in sequence and not to skip concepts to compensate for missed time. But the snow days mean rethinking priorities, she said. “Definitely some reorganization must occur,” she said.

Principal James Fernandez at Albert Einstein High School in Kensington said that for some students, the toll of missed days includes not only academics but also social interaction and subsidized meals, which can’t be made up. “In our case, we’re mentoring in addition to teaching,” he said.

Parent Connie Kiggins of Chevy Chase says she has seen the effects of the compressed schedule in more work being sent home. Her seventh-grader was up until nearly 1 a.m. with a social studies project that she said otherwise would have been finished in class. Her younger child, in fourth grade, received extra homework in advance of a predicted snow day, which she felt was reasonable, but overall with snow days happening so often, “it’s been very disruptive.”

Other parents say they have had a hard time keeping students motivated with school schedules in such flux.

John Hoffmann, an earth science teacher at Woodgrove High School in Purcellville, said he is running three weeks behind in the curriculum as end-of-year Standards of Learning exams approach.

“If I were a younger teacher, I would be pretty panicked about how I was going to finish the rest of the year,” he said. But after 25 years teaching, Hoffman knows how to take a 10-day academic unit and fit it into seven days. Unfortunately, he said, most of what gets lost is the enrichment or hands-on activities that students tend to enjoy.

Last week, he cut out a computer simulation that lets students move the continents around to see what they would have looked like 250 million years ago.

Gabrielle Carpenter, director of school counseling at Tuscarora High School in Leesburg, said her office has been filled with seniors concerned that their grades will suffer from deadlines blown during canceled classes. “We can assure them 100 percent that things will be adjusted,” Carpenter said.

She said teachers have been advised not to penalize students, particularly since some students don’t have access to the computers or other resources they need to complete assignments at home. In the meantime, she said, there is “across-the-board higher anxiety” about how to prepare students for looming tests.

Teachers at Park View High School in Sterling have been using class Web sites to post materials and correspond with students, and some teachers have been posting videos of lessons to keep the instruction going, said principal Virginia Minshew. “The technology is really helping,” she said.

For older students, spring testing is an issue. Some school districts are considering asking the College Board for delays in administering Advanced Placement exams, while others have requested delays for state testing.

Districts are dealing with the closings differently in terms of scheduling. Some already have extended the school year into summer break, and others have changed teacher work days into full instructional days or have canceled some scheduled holidays. Montgomery is seeking a state waiver that would allow the district not to make up some of its snow days.

Some parents suggest that the winter’s difficulties should inspire a broader conversation about how to handle snow days.

Daneene Chadwick, president of the Parent-Teacher-Student Association at Briggs Chaney Middle School in Montgomery, said the spate of closings raises the question: Should the district have a plan to continue education online in some form during inclement weather?

“I think that’s something that can’t be ignored when you’re looking at this number of days,” she said.

For all the school time lost in the Washington region, the Western Maryland schools of Garrett County have lost more: 20 days claimed by snow and extreme cold, officials said, nearly a full month of classes.

“The biggest thing we see is that kids get out of a routine, and it’s hard to get back into a routine when you’re in school two days and out of school three days,” said schools spokesman Jim Morris.

Ovetta Wiggins, Emma Brown and T. Rees Shapiro contributed to this report.