PITTSBURGH — Teachers in three Pennsylvania school districts went on strike Tuesday.

Union representations and officials in the Shaler Area School District met for about six hours Monday with a state-appointed mediator but were unable to reach agreement. Melissa Ravas, president of the Shaler Area Education Association, said teachers were expecting a new offer Monday but didn’t receive one.

Shaler schools Superintendent Wesley Shipley said the next negotiating session is planned for Wednesday evening.