Thousands of students across Northern Virginia enjoyed time off last week, allowing them go sledding, watch television or, at least in Loudoun County, celebrate a round of canceled midterm exams.

But as they return to school today, many students can look forward to school and more school as some districts make up for lost time with altered schedules.

Here’s a round up of how snow days affected school calendars in your district:

Alexandria: Students will be required to attend school on previously scheduled professional workdays — March 14 and April 11 for students at schools with a traditional calendar, and Feb. 28 and March 21, for students who attend schools with modified, year-round calendars. If there are any more closures, officials may add extra minutes to the school days.

Arlington: Officials already adjusted the early-release schedules for some elementary schools, and they are studying the calendar and may need to make some further adjustments after last week’s weather-related closures, schools spokesman Frank Bellavia said.

Fairfax: Officials have scheduled make-up days on President’s Day, Feb 17, and April 7. If school is canceled again, students will have to dip into their summer vacation with an extra day on Monday, June 23.

Loudoun: There are 15 extra days built into the school calendar. So far, school has been closed for eight days and delayed for two.

Prince William: The system started the year with about eight snow days on reserve. But after last week’s closures, there are only 1.5 extra hours left before the district dips below the state minimum required instructional hours. “We are really down to the nitty gritty,” schools spokesman Phil Kavits said. “Our superintendent and staff are looking carefully at the options . . . and given the way the winter looks, we will probably need some more time here.”