Brooke Petersen would have rather spent Friday teaching inside her Dedham classroom instead of walking a picket line. But the middle school teacher said the teacher union's strike has been "a long time coming."

"We're all here, at the end of the day, to support our students. No matter what," said Petersen, who teaches English as a second language. "The only way to do that is to be outside of the schools and rally until we can get the proper support that we need to help them."

Students and parents picketed alongside their educators. Car and truck horns honked in support, too.

The Dedham Education Association said it wants a contract after nearly two years of negotiations with the school district. The union contended Friday that there's an impasse when it comes to pay, professional development, healthcare and sexual harassment protections.

Petersen said it's paramount the new contract provide better protections against sexual harassment.

"I myself have been subjected to pretty foul language," she said. "And I've seen some of my coworkers have to file against this particular issue."

Union President Tim Dwyer said the district "absolutely refused to listen to our proposal on sexual harassment policy."

In a contract negotiation update posted online Wednesday, Dedham Public Schools outlined its offer to establish a joint committee with the union to renew and update the district's sexual harassment policy.

"The District recognizes the priority of this issue for teachers, and maintains that formal policy language in a collective bargaining agreement is not the appropriate venue for addressing this issue," the update said.

The Wednesday memo also outlined other offers by the district, including wage increases, stipends for implicit bias training and changes in professional development. The union rejected the offer without countering.

Dwyer said teachers would end up working more hours and pay more for healthcare under the school district's proposal. He said the strike is about getting dignity as well.

"We haven't been treated with proper respect," he said.

In a statement released Thursday, Dedham School Superintendent Michael Welch canceled classes for students but said teachers and other school employees were expected to show up to work for an "in-service day."

In the statement Welch said:

As a district, we are saddened that our educators have chosen to consider this drastic and harmful action. We wholeheartedly appreciate and support our wonderful educators. They have shown unwavering enthusiasm and engagement in the classroom, and they have been propelling the incredible advancements we’ve made in our schools over the last few years, despite this ongoing difficult contract process.

The Massachusetts Department of Labor Relations on Thursday ruled that the strike is illegal, citing state law that forbids public employees from striking.

But teachers said they're prepared to face the consequences, and some students have their backs.

High schooler Jill Scaramuzzo said she felt teachers should have their demands met.

"I think the teachers deserve whatever they're asking for," she said. "I think they should do whatever they need to do to stand up for what they believe in."

Joanne Scaramuzzo, Jill's mom, said she thinks her daughter is learning a valuable lesson, too.

"I think it's an educational opportunity for her, at this stage, to see how people come together — the teachers, the community — when they really believe that something is right," she said. "They do so much for our kids, and we want them to feel like they're being well-taken care of."

But she hopes the resolution comes sooner rather than later. Middle school teacher Petersen hoped so, too, but said she is prepared to picket beyond Friday.

"I think we sent a pretty strong message today, and we will continue to do so in the weekend."

With reporting from WBUR's Newscast Unit and Roberto Scalese