Chicago public school teachers and their supporters rally at the school district's headquarters earlier this week.

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NEW: Deal is "an honest and principled compromise," mayor says

Union president "very comfortable" with teacher eval issue under proposed deal

Union officials will meet Sunday to vote on whether to end the strike

Schools remained closed Friday

Chicago CNN  — 

The Chicago Teachers Union and the city’s school board reached a tentative agreement Friday in their dispute over new contract terms that has closed public schools for 350,000 students.

Despite the possible deal, union president Karen Lewis cautioned that the strike, in its fifth day Friday, is not yet over.

Union officials will meet between now and Sunday to draft specific language on a “framework for an agreement.” They will present the document to a special committee of union representatives, at which time a majority vote will be taken on whether to suspend the strike.

“Our delegates were not interested in blindly signing off on something they have not seen,” Lewis said.

However, Lewis was optimistic that the deal would be finalized.

“We think it’s a framework that will get us to an agreement, but we are not quite there,” she said, adding she is “hoping and praying” students will be back in the classroom Monday.

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Chicago School Board President David Vitale was similarly positive about moving forward.

“We have in place frameworks around all of the major issues that should allow us to conclude this process and to conclude it in time for our kids to be back in school on Monday morning,” he said.

Lewis declined at a news conference Friday afternoon to discuss details of the agreement.

A source close to the negotiations said some of the terms include: keeping the current length of school year and school day; giving principals the freedom to hire their own teachers; and, chief among the dispute’s sticking points, updating the teacher evaluation system for the first time in 40 years.

Lewis said Friday afternoon that she was “very comfortable” with the teacher evaluations issue under the proposed framework agreement.

Chicago Mayor Rahm Emanuel praised the progress made between the two sides after days of sometimes contentious meetings.

“This tentative framework is an honest and principled compromise that is about who we all work for: our students,” Emanuel said in a statement.

“It preserves more time for learning in the classroom, provides more support for teachers to excel at their craft, and gives principals the latitude and responsibility to build an environment in which our children can succeed. Now, our most important work continues: providing every child in every community of Chicago an education to match their potential.”

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New hope emerged Thursday after days of sometimes contentious meetings between the teachers union and the school board.

The union, which represents nearly 30,000 teachers and support staff, called the strike on Sunday night.

The union previously said the two sides had been close to a deal on pay, but far apart on teacher evaluations, benefits and other issues.

Teachers were concerned about job security in the wake of a new program that evaluates them based on their students’ standardized test scores. Union board member Jay Rehak called the program “data-driven madness.”

As many as 6,000 teachers could lose their jobs under the evaluation system, said Lewis, who had called the system “unacceptable.”

The mayor’s office, the city and school officials have questioned that job-loss figure.

The median base salary for teachers in the Chicago public schools in 2011 was $67,974, according to the system’s annual financial report.

Parents have been anxious for a resolution of the strike.

“There is … frustration, foremost,” said Sarah Liebman, the mother of two children in city schools. “It’s really affecting the kids right now.”

Ahead of the strike, the Chicago Public Schools crafted a plan – one criticized sharply by union leaders – trying to give parents like Liebman options until teachers return to work.

The city’s famed public transit system offered free rides for students to move between so-called “safe haven” sites. Chicago’s parks department resumed camp-style sports, art and nature programs at dozens of its locations, while the public library system set aside computers in its facilities for students to use.

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CNN’s Sarah Aarthun contributed to this report.