CHICAGO (CBS) — A day after saying there had been “a lot of progress” in Friday’s negotiations with the Chicago Teachers Union, a top Chicago Public Schools official accused the union of an unspecified “breach of trust,” but CTU President Jesse Sharkey said he remains optimistic a deal can be reached to end the ongoing teachers’ strike by Monday.

As CPS and CTU negotiators gathered at Malcolm X College for another bargaining session Saturday morning, CPS chief education officer LaTanya McDade said there had been an unspecified “breach of trust” by the union after Friday’s negotiations were completed.

“We left the table last night really determined to bridge the divide across the table on some of the really big key issues that are still at play, that we’re going to be addressing this morning. Following the close of negotiations yesterday evening, there was a breach of trust that gives us some serious concern as we come back to the table this morning. Our plan is to address that at the table, and we will continue to bargain in good faith and work really hard to get to a place where we can reach an agreement that gets our students back in the classroom as soon as possible. We will be giving updates throughout negotiations,” she said.

McDade did not elaborate on the “breach of trust,” and following a CTU rally in Union Park later Saturday, Sharkey said he did not know what McDade was referring to, but said negotiations were in a “sensitive spot.”

“I’ve been through this before. It’s not uncommon when negotiations are at this stage for nerves to get frayed, for emotions to be high, and we just have to manage our emotions, and keep at the hard work that is required to go through, and try to get a contract that represents fairness in our schools,” Sharkey said.

However, he said he remained optimistic about the possibility of coming to an agreement to end the strike in time for classes to resume on Monday.

“We’re serious about trying to get to a deal. We obviously need to be able to come back and look our members, and the students, and the community, and the city of Chicago in the face and say we did something good for schools. That’s going to be the standard that we’re going to hold to this, but we’re going to work hard, and I think it’s within reach,” Sharkey said.

Teachers have been on strike since Oct. 17, and students have missed seven days of class as a result, matching the length of the last Chicago teachers’ strike in 2012.

On top of the pressure to get students back to class, deadlines for college applications are around the corner and student athletes are missing out on state finals.

Yet another added pressure is the issue of healthcare — sources within the CTU tell CBS 2 that teachers were told their healthcare would expire by Nov. 1.

Sharkey said the remaining issues under discussion include major topics like salaries, class sizes, and staffing.

“Obviously, this is the issues that are the most difficult, the ones that we care a lot about, and they care a lot about,” he said.

As negotiators were at the table on Saturday, hundreds of CTU members — joined by school support staff represented by SEIU Local 73 — rallied in Union Park on the Near West Side. SEIU support staff also have been on strike since Oct. 17.

Also on Saturday, the Jones College Prep cross-country team attended a state regional meet in Lincoln Park, a day after a Cook County judge ruled that they could not participate in the state playoffs because of the strike. The team had sued to challenge an Illinois High School Association policy prohibiting sports teams from participating in competition of any kind during a strike.

Because the Jones students could not run in the regionals at Lincoln Park, they held their own meet after the official race.

Runners said they feel heartbroken and disappointed with not being able to compete in the state playoffs, and possibly missing out on scholarship money, but they don’t hold any ill will toward striking teachers.

Sharkey said one of the most difficult parts of a strike is the impact on student athletes who train hard to compete, but cannot do so due to IHSA rules.

“Students who are competing in big games, that’s going to be a more meaningful and important part of their experience in school than any math test,” he said. “I’m genuinely sorry for the disruption this strike has caused for students. This is something that wasn’t their fault, and all I can say is that what we are trying to accomplish is we’re dealing with short-term disruption and difficulty in the hope of trying to get conditions which improve public schools in Chicago for a long time.”