Chicago public school teachers began manning picket lines instead of classrooms Monday, launching the first teacher strike in the city in 25 years.

The strike, announced Sunday night, left about 350,000 students without schools to attend and parents scrambling to find alternatives. The union that represents nearly 30,000 teachers and support staff in the nation's third-largest school district called the strike after negotiators failed to reach a contract agreement with school administrators despite 10 months of negotiations.

Below, we break down the key issues that are keeping the teachers out of the classroom, what the teachers are asking for and what the schools are willing to offer.

Compensation and health care benefits

One of the key issues is salaries and benefits for teachers and their families.

What the teachers want: to maintain their existing health benefits, as well as salary increases.

"Recognizing the Board’s fiscal woes, we are not far apart on compensation,"  the Chicago Teachers Union said in a news release. "However, we are apart on benefits."

What the Chicago Board of Education is offering: a deal that would increase salaries 16% over four years. The average teacher salary in Chicago was $74,839 for the 2011-12 school year, according to the district. The total salary increase would equal $380 million over four years. That includes "modified step increases that both reward experience and provides better incentives for mid-career teachers to help keep them serving in the Chicago Public School system," according to a news release from the school system.

"The Board is calling for a modification to the health care plan funding that will freeze all employee health care contributions for single and couple plans with a small increase in family contributions of no more than $20 a pay period in addition to a small increase in emergency room co-pays," the school system says. "67% of all CTU members will not see a change to their healthcare."

Job security

Another major issue is making sure teachers will know their jobs are safe amid the likely closing of several schools over the next couple years. Teacher issues center on what options will be available to them if they are laid off, as well as how they can be promoted.

What the teachers want: more teacher training and help for laid-off workers.

“We want job security. Despite a new curriculum and new, stringent evaluation system, CPS proposes no increase (or even decreases) in teacher training. This is notable because our Union through our Quest Center is at the forefront teacher professional development in Illinois," the union says. "We have been lauded by the District and our colleagues across the country for our extensive teacher training programs that helped emerging teachers strengthen their craft and increased the number of nationally board certified educators."

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The union notes that "while new Illinois law prohibits us from striking over the recall of laid-off teachers," it does not plan to sign an agreement until both sides discuss the issue and implement a plan.

What the Chicago Board of Education is offering: The board has announced plans and opportunities for laid-off workers but only a willingness to discuss opportunities for promotion.

The school system notes that it has addressed concerns about teachers displaced by school closings, turnarounds or phaseouts, and other reasons.

If a school is closed, Chicago Public Schools says, teachers will "receive a job at a school receiving their students if there is a vacancy; placed in a reassigned teacher pool for five months or may elect to receive a three-month lump sum severance; or placed in a Quality Teacher Force Pool in which teachers who apply for positions shall be entitled to an interview and explanation if not hired."

If a teacher is displaced by turnarounds or phaseouts, they will be "placed in a reassigned teacher pool for five months or may elect three-month lump sum severance." Teachers displaced for other reasons will "have recall rights for one year for the same unit and position and will be offered interim assignment in substitute teacher pool."

As for moving up within the system, the Board of Education says the union should work with it "to increase promotion opportunities and identify differentiated compensation models that have worked in other places."

New teacher evaluation system

As many as 6,000 teachers could lose their jobs under a new evaluation system based on standardized test scores implemented by the school district, Chicago Teachers Union President Karen Lewis said. Statistics from the Chicago Public School District and the state show that Chicago children perform poorly compared with the rest of students, with 10% to 20% more students not meeting the goals compared with rest of the state in reading, math and science during the 2010-11 school year.

What the teachers want: a change to the new evaluation system for teachers.

Lewis called the new system "unacceptable," saying that too much emphasis is being placed on testing scores.

"This is no way to measure the effectiveness of an educator. Further there are too many factors beyond our control which impact how well some students perform on standardized tests such as poverty, exposure to violence, homelessness, hunger and other social issues beyond our control," the union said in its news release.

What the Chicago Board of Education is offering: to help get the new system in place and reach required standards.

"The Board has proposed to work jointly with CTU to fully implement REACH Students and maintain performance standards and student growth requirements," it said in its release. "This proposal will also allow CPS and CTU to study REACH’s implementation jointly and make adjustments as needed."

Opinion: U.S. needs more strikes

My view: The whole world is watching Chicago