It's been an above-average winter for snowfall in St. Louis, and that's wreaking havoc with the schedules for area school districts.

By state law, Missouri students have to be in class for at least 174 days and 1,044 hours. Most districts build a few extra classroom days into the schedule in order to be able to call school in case of bad weather.

But the series of winter storms that have struck the last two months have pushed some districts, like suburban Ladue, to the limit of those days.  Others, like Parkway, will already have to make up days in June.

Marcia Chappelow, Ladue's superintendent, says she won't let the possibility of a slightly shorter summer break stop her from calling school if she feels it's necessary.

“If I’m going to err, I will err on the side of safety," she says. "I know that people have plans made, but there are different ways that you can make up time."

The St. Louis Public Schools also aren't worried about extending the school year into June, says district spokesman Patrick Wallace. (The SLPS have already canceled six days of class this year, and will have to make up at least four of them.) What concerns officials, Wallace says, is the loss of instruction time before state exams that measure adequate yearly progress.

"You compare this year’s test scores to last year’s test scores, the students last year would have that many more instructional days, so it kind of puts the test scores from this year at a disadvantage," he says.

For that reason, the district and its teacher's union agreed on Thursday to cancel a planned half-day of professional development on Friday to give students a full day in the classroom instead.

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