(AP Photo/Nam Y. Huh) (AP Photo/Nam Y. Huh)

The messy winter weather in many parts of the country have forced schools to close over and over, forcing school districts around the country to alter their schedule for the year to find time to make up for lost instructional time. But is that really necessary? How much do kids lose when school is closed because of bad weather?

It seems like the common-sense answer would be that it depends on how many days, and it depends on how much work teachers dump on students when they return to school (which would be fine for kids who can work fast but not so much for those who can’t). But a 2012 study from a Harvard University researcher, which the school has just pulled out to publicize, says that isn’t the case.

The study, titled Flaking Out: Snowfall, Disruptions of Instructional Time, and Student Achievementby Joshua Goodman, an assistant professor of public policy at Harvard’s Kennedy School of Government, says that school closures due to inclement weather do not actually affect student achievement as measured by scores on the standardized Massachusetts  Comprehensive Assessment System. Individual absences do.

Goodman began the study after the Massachusetts Department of Education asked him to “crunch numbers” to determine student achievement losses because of snow days. He looked at earlier research on the importance of instructional time, and found mixed results, and then examined a mountain of data for students in Massachusetts in grades three through 10 from 2003 to 2010, looking at school closures, individual absences, and standardized test scores.

Here’s what he concluded:

*The closure results suggest either that instructional time does not matter or, more likely, that schools are prepared to deal with coordinated disruptions like snow days.

• Schools do not, however, seem to deal well with less extreme disruptions in which only some students are absent…. Estimates suggest that absences explain 8-20% of the achievement gap between poor and nonpoor students.

•These results are consistent with a model in which the central challenge of teaching is coordination of students. One policy implication is that schools may be under-preparing for such disruptions.

•Of course, schools have little control over the weather. Other sources of variation in absences may be more  interesting from a policy perspective: illness, transportation problems, domestic trouble. Constructing  instruments from these is, however, tough.