Michelle Gunderson used to look forward to her weekly training sessions about how to work with struggling readers.

One morning per week, she and her fellow first-grade teachers at Nettelhorst Elementary School in Chicago would cycle through each other’s classrooms to discuss useful strategies and to see the visual aids others were using up close.

But then Mayor Rahm Emanuel mandated a seven-hour school day for all students, pointing to research tying more time in school to better academic outcomes. Under pressure to spend more time in front of students, teachers had to abandon the training sessions.

With 840 students to instruct, the school’s hectic schedule hasn’t allowed for shared planning time to serve as a replacement. And teachers also have less time during the school day to complete essential responsibilities such as writing lessons and grading tests.

“The nature of teaching is that you have to pace yourself so you have enough energy to get up and do it the next day,” Gunderson said, a veteran with 20 years of experience in the classroom. “If you spent all night planning and grading papers, what do you have to give the children the next day? We have to be able to reserve our energies so our instruction is effective.”

Gunderson’s experience reflects a fundamental tension in schools with expanded learning time for students: Research suggests that more time in school boosts students’ skills and long-term prospects, but adding productive time to students’ days often means cutting time from their teachers’. And that lost teacher planning and training time, research shows, also matters.

“It really is a balance. More time is only as good as it’s being used,” said Scott Barton, the principal of a California charter school whose model includes additional time for students and teachers alike. “To use that time wisely, we have to make sure that our teachers are prepared.”

New York City’s recent experience highlights the tug of war that can play out around learning time.

The city’s 2005 contract with its teachers union added 150 minutes per week of small-group instruction for struggling students, in keeping with then-Mayor Michael Bloomberg’s “Children First” education agenda. “We are taking 300,000 children who are performing below average, and as of today they are going to have an extra period, four days a week in classes of 10 or less,” he said at the time.

But when Bloomberg’s successor, Bill de Blasio, negotiated a new contract with the union in 2013, he took a different approach and rolled most of that time back to make way for teacher training and collaboration.

The teachers union hailed the change. “We have to train teachers so that the time they’re spending with students is much more effective and valuable,” union chief Michael Mulgrew said at the time. “Versus doing, once again, this political punch line — more time with the student. Let’s make it better time with the student.”

But the tradeoff left some educators scratching their heads. “I honestly have never met one teacher who thinks the solution to the educational crisis is less time with students and more time in PD,” one teacher wrote on his blog.

The same balancing act is playing out in thousands of schools across the country that have extended the school day, according to Jennifer Davis, co-founder and president of the National Center on Time and Learning, a nonprofit that advocates for expanded learning time.

Davis said schools that are strategic about how to allocate time can optimize their schedules to meet both student and teacher needs. About half of the 2,000 schools her group tracks offer additional time for students and teachers alike, she said.

“I’m not saying it’s easy,” Davis said. “There are hard trade-offs, but there are ways to work it out.”

The Preuss School, the charter secondary school in La Jolla, Calif., that Barton runs, is one school where managing those tradeoffs has been a goal from the beginning. Founded in 1999 with more time for students and teachers as a key part of its model, Preuss requires students to be in school for 198 days a year, rather than the more typical 180 days.

In addition, Preuss teachers teach for six of the eight class periods per day. A teacher’s two free periods are blocked together for a daily 90-minute prep period, which is frequently used as collaborative planning time across departments or grade levels.

And the school has a later student start-time each Friday, providing all teachers with 105 minutes to collaborate and learn from one another every week.

“We felt from the beginning that there has to be time for teachers if we have more time for students,” Barton said. “Teachers need time and we need to build it in — not make it after school.”

Janis Gabay, an English teacher at Preuss and the 1991 National Teacher of the Year, serves as her department’s chair and said the Friday professional development sessions are unlike anywhere else she’s worked.

“When I worked in the large school district, staff development was kind of a monthly thing, if that, where you trotted out a speaker and you had people who sat in the back and wanted to grade papers,” she said. “Here, it’s a way to stay connected with one another. It’s where we’re encouraging the reflective teacher and asking things like ‘What have you struggled with? What are you curious about?’”

Charter schools like Preuss tend not to be bound by union contracts and so have the most flexibility in reworking schedules to balance the needs of students and teachers.

But traditional schools are finding ways to split the difference, as well.

Oakland, Calif., has found a way to resolve the tension by combining expanded learning time offerings in the summer for both.

Typically, summer school is a time for bare-bones instruction to ensure that students get the basics that they did not pick up during the school year. But last summer, Oakland hired coaches to work with English and math teachers as they worked to tie their teaching to the Common Core standards for the first time.

Tamrya Walker, who is a math teacher and instructional coach in Oakland, said one of the benefits of training during the summer is the smaller class size and fewer requirements placed on the teachers.

“There’s not as much stress in terms of assessment,” she said. “Teachers can focus on helping kids.”

A new program in Denver is taking the same approach. The district recently launched a three-week laboratory summer program for teachers to try out new strategies, particularly around how to tailoring instruction to individual students.

Signs of balance are even emerging in contracts between districts and their teachers union, traditionally an arena for tugs of war over time because they set parameters for how teachers’ days are spent. In December, Boston negotiated a new contract that added 40 minutes a day at dozens of schools and also doubled teachers’ planning and training time.

“Boston public schools have been saying for many years that we need a longer school day,” said Michael O’Neill, chairman of the city’s school governing board, said when announcing the contract terms. “But a longer day isn’t effective unless you also transform the quality of the education.”

Boston teachers at participating schools saw nearly $5,000 raises as a result of the added time.

In districts with less fiscal flexibility, figuring out how to balance teacher and student time has been more of a challenge.

In Philadelphia, School Reform Commissioner Bill Green is advocating for a longer school day in the district’s next teacher contract. “It’s fairly simple,” he said. “All of the research indicates that longer school days or years have a positive impact on the achievement of urban students.”

Green is also arguing that state law requires Philadelphia to increase instructional time by nearly half an hour a day — an interpretation of the law that the teachers union is contesting. But he has said the cash-strapped district cannot pay teachers any more.

“To expect that the district is going to be able to attract and retain teachers as long as they totally disrespect them as professionals is unconscionable,” Philadelphia teachers union president Jerry Jordan said earlier this year, reacting to Green’s longer-day push. “It’s not going to happen.”

Back in Chicago, where the 2012 contract resulted in the city’s first teachers union strike in 25 years, teachers hope a new contract will better balance time for students and time for teachers.

Time isn’t the biggest issue in ongoing negotiations, which appear likely to extend beyond the June 30 contract expiration. Instead, the city and teachers union are locked in conflict about how teachers should be evaluated and how likely layoffs will happen.

Still, Gunderson said she hopes an eventual contract adds resources so that teachers can work together to make the longer school day effective.

“Without the time we have together, I don’t have as much of a chance to connect with my fellow teachers in terms of mentoring,” she said. “Here I am with years of craft knowledge that I would love to be able to give to my fellow teachers, but I’m not afforded the time to anymore.”

This story was produced as a collaboration among all news organizations participating in the Expanded Learning Time reporting project.