PROVIDENCE — The Providence Teachers Union, the Providence schools superintendent and state commissioner of education have agreed to work with a mediator to resolve their differences over a teacher-hiring plan that effectively replaces seniority.

U.S. District Court Judge William E. Smith issued the 90-day stay last week. In August, the union filed suit to prevent the district from abolishing seniority as the primary method for filling teacher vacancies.

Supt. Thomas Brady imposed the change after former state Education Commissioner Peter McWalters ordered the district to create a more rigorous method of hiring teachers, which calls for an extensive interview and application process. The district moved to this new “criterion-based” hiring system in six pilot schools this fall.

Teachers union president Steve Smith called the judge’s order a win for both the union and the school administration.

“We have been looking for the chance to be on equal footing with the district,” Smith said Thursday. “We want a forum to have our ideas vetted. This spring, the superintendent wasn’t interested in negotiating with us. McWalters wasn’t interested in having us at the table.”

Marc Gursky, the union’s lawyer, said Education Commissioner Deborah A. Gist is checking her contacts to see who might be a good fit. A mediator typically brings both parties together, keeps the talks on task and helps them reach a resolution.

“Failing that,” Gursky said, “we might use an expert in the field of elementary and secondary education, plus a mediator.”

Brady said that the district’s lawyer is looking into hiring a nationally recognized mediator.

“In the meantime,” Brady wrote, “we remain committed to moving forward with our full implementation of the commissioner’s order, which puts the needs of students foremost in our hiring and assignment practices.”

In its suit, the 2,000-member teachers union is challenging the authority of the state education commissioner to order the district to create a new hiring practice, a move the union says should be handled within collective bargaining. The union filed its complaint in federal court because it claims that the commissioner’s order violates both the federal No Child Left Behind Act and the U.S. Constitution. The suit names Brady, School Board President Robert Wise and Gist, who began the job four months ago.

Until now, vacancies have been filed based on seniority — a practice that critics say has created a lot of turbulence and staff turnover. Under the old system, whenever there was a vacancy, a teacher with the most seniority bumped or dislocated someone with less.

Smith said on Thursday that the union never opposed the shift from seniority per se. Rather, teachers want the opportunity to shape the new criteria by which teachers will be hired. The union says that Brady’s hiring practice “eliminates in its entirety impartial and objective decision-making” because it requires that the district only offer an “adequate explanation” for teacher assignments.

Word that both sides were willing to sit down together came as welcome news to two local grass-roots organizations, Young Voices and the East Side Public Education Coalition, which had launched a petition to pressure the union to drop its lawsuit. Karen Feldman, codirector of Young Voices, a youth empowerment group, said she was very pleased that mediation was in the offing.

“We are not anti-union,” she said. “We’re not anti-anything. Our goal is to put the most effective teacher with students who need the most. Our hope is that both parties meet in good faith.”

lborg@projo.com