CHICAGO (CBS) — Classes have been canceled through Tuesday for two high schools in northwest suburban McHenry, after teachers and the school district failed to reach a deal during a 12-hour negotiation session on Sunday.

Teachers at McHenry Community High School District 156 have been on strike since Thursday. The two sides met Sunday in an effort to reach an agreement on a contract, and made some progress toward a deal, but ended their talks around 1 a.m. Monday without a contract.

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“We’re working really hard to try to get something accomplished, but we still also have a ways to go. So I think both sides are disappointed that … we couldn’t come to an agreement,” said Heidie Dunn, spokeswoman for the McHenry Community High School Educators’ Association.

The main sticking points are salaries and health insurance premiums.

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The teachers union and the district won’t return to the negotiating table until Tuesday, meaning more than 2,500 students at McHenry West and McHenry East high schools will be staying home again Monday and Tuesday.

The two sides won’t meet Monday, due to a previously scheduled school board meeting. The union said teachers plan to be at the meeting to make sure their voices are heard.

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The 150 teachers planned to walk the picket lines Monday and Tuesday outside both high schools.