One sticking point in the Chicago strike: teacher prep time. Here’s how the city stacks up.

The Chicago Teachers Union’s push for smaller class sizes and more nurses, social workers, and librarians would bring conditions in Chicago’s schools closer in line with those in other cities nationwide.

But when it comes to how much time teachers get during the school day to prep, or do work that does not involve teaching students, the union is seeking a change that would set the city apart — and potentially add to its ranks.

The current union contract gives Chicago elementary school teachers an hour of uninterrupted prep time every day. The union wants its new contract to add 30 additional minutes of prep time for all elementary school teachers at the start of every school day.

No other elementary school teachers in big-city districts are guaranteed 90 minutes a day of prep time, according to the National Council on Teacher Quality, which maintains a database of teachers union contract terms. In a 2017 analysis, the group found that the district with the most prep time was Anne Arundel County Public Schools in Maryland, where teachers get an hour and 22 minutes of prep time daily, half to be spent in collaboration with their colleagues.

More commonly, teachers across the country are assured an average of 45 minutes a day of prep time, but many contracts don’t provide even for that.

Falling in line with other districts, of course, is not the Chicago Teachers Union’s goal. The union enjoys a reputation as one of the most progressive in the country, and negotiating a contract that makes Chicago teachers the vanguard on a core classroom issue would be a win.

“Any time teachers in these large districts go on strike and win concessions they can inspire other people,” said Kency Nittler, NCTQ’s director of teacher quality. “Around prep time, it would certainly give other unions the opportunity to point to Chicago and say, ‘Look at what these teachers are getting. Why don’t we get that here?’”

Chicago officials say that granting the union’s request would cut into instructional time for students. But the union has said the district could handle the 30-minute morning-planning block in other ways, such as by having students work with other school staff or paying teachers more to come in 30 minutes earlier.

“Overall, teachers having more prep time is a good thing for students, and for teachers too, so from the union’s perspective, pushing for more prep time is always going to be a good thing,” Nittler said. “The district’s job is to fit however much prep time they can into a given school day.”

On Tuesday, nine days into the union’s strike, Chicago Public Schools CEO Janice Jackson said the district could not come up with ways to give the union what it wants without reducing class time for students.

“What’s holding this up now is a set of political issues, and an effort to try and cut instructional time, which we cannot agree to,” Jackson said.

Increasing prep time can be a boon for unions even beyond the benefit that individual teachers derive from getting more time to plan, grade papers, and collaborate with colleagues. Katharine Strunk, a researcher at Michigan State University who studies unions, said the Chicago demand might reflect how unions are responding to the pressure induced by a 2018 U.S. Supreme Court decision that eliminated compulsory union membership.

“If the union understandably wants more time to help teachers prepare for their school day, but they don’t want to extend the time that teachers are at school, and we don’t want to shorten instructional time for kids because we know that time with teachers is good for them, we need to find other people to staff kids’ classrooms,” Strunk said. “And those people are going to be union members.”

The Chicago Teachers Union has not specified exactly who it believes should work with teachers during the new prep period if one is created, beyond suggesting that art and music teachers could play a role. It also has not publicly squared its demand with other contract provisions it appears to be winning to insulate some support staffers from tasks beyond their core responsibilities.

But it’s clear that the union faces membership issues even beyond the pressure introduced by the Janus ruling. The city’s declining population has driven down enrollment at city schools and reduced the number of teaching positions needed. An expansion of charter schools has created more teaching positions that are not unionized. (The union is working to organize teachers at city charter schools, with increasing success.) And a five-year moratorium on school closures recently expired, making the prospect of more closures — and eliminated teaching positions — loom large against the contract negotiations.

Three of the Chicago Teachers Union’s biggest demands had staffing implications: to reduce class size, add support staff, and increase prep time.

“All of those things are good for kids,” Strunk said. “But they also all drive up union membership.”

The city has agreed to some of the union’s demands on the first two issues, and city officials say they also offered a compromise on prep time when they withdrew a proposal that would have let principals determine how more of it is used.

Whatever happens with the prep time contract dispute, many teachers say their experience is that contractually guaranteed prep time is never as long as it’s supposed to be.

Nate Ramin, who teaches sixth-grade social studies at McPherson Elementary School in Lincoln Square, said he usually spends the first few minutes of his prep period escorting students to another classroom. At a previous job, he was frequently called during his prep to cover for other teachers. Ramin teaches several students with disabilities and says co-planning with special education teachers and attending meetings about those students take considerable amounts of planning, giving him less time to work on his actual lessons.

He pointed out that even if elementary school educators get 90 minutes a day of prep time, they would still fall short of the city’s high school teachers, who are guaranteed 500 minutes of prep time each week. “But it’s not an us versus them thing,” Ramin said. “We’re together on this.”

Cassie Walker Burke contributed reporting.