Most schoolkids count down the hours till the final bell rings each day, as well as the days until summer. Now, schools will likely begin counting hours more closely and days more loosely. And, more important, a state law about when school can be in session could face an overdue challenge.

Public schools in New York now must operate at least 180 days a year, which makes sense. They cannot begin before September or end after late June, which makes no sense. But neither rule was a big issue until the religious and ethnic composition of school districts began to change.

As districts on Long Island have become more diverse, their calendars and the official holidays they observe have gotten more controversial. But the problem mostly isn’t anti-diversity folks arguing that soon schools would close almost every day for someone else’s holiday, though that has come up. The big problem is fitting in new breaks without blowing through the September-to-June window.

Schools here have taken off for Christian and Jewish holidays for decades. But over the past few years, movements to add the Lunar New Year, the Hindu festival of Diwali and the Muslim Eid al-Adha and Eid al-Fitr have caused tension. The calendar is so tight that at some point, either no new holiday can be respected or an established one must go.

One easy stopgap the state Board of Regents says it will approve at its March meeting is to require schools to teach a certain number of hours annually rather than days. This would give schools partial credit for days when they shut down early for weather, and create more opportunity for teacher training, recess and parent conferences.

This is the easy fix, but it’s not the best solution for fitting in all the holidays some schools need. Or for fitting in all the instruction some students need. Because of that, state Education Commissioner MaryEllen Elia said she will propose legislation next year to change the state law that schools must not be open before September or after late June.

That law is outdated and largely exists thanks to industries that thrive on traditional summer vacations, like camps and tourist spots, exercising political clout to keep them. Many teachers also support the traditional break.

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But studies show summer breaks might need to be shorter to improve academic outcomes, particularly in low-performing districts where kids can lose months of learning each summer.

“There are certain districts where camp-going is a big deal,” Elia said. “But there are certain areas where no such opportunities exist.”

Elia is right to question a law that keeps high-needs school districts from adopting longer school calendars in order to prop up pricey camps kids in those districts will never see.

Lane Filler is a member of the Newsday editorial board.