Instructors march to Denver Public Schools headquarters to deliver Valentine's Day cards Wednesday. Teachers walked off their jobs Monday, the first strike by teachers in Denver in 25 years. (David Zalubowski/AP)

Striking teachers in Denver reached an agreement Thursday with the school system that increases salaries, ending the latest in protests by educators that have swept the nation.

Thousands of Denver teachers walked off the job Monday after reaching an impasse with Denver Public Schools officials over pay, the first strike in 25 years. Schools remained open but woefully understaffed during the strike, and preschools closed. It is the second time Colorado teachers have walked out in protest. Last year, teachers across the state staged a one-day rally at the state Capitol to press for more school funding.

Denver was the first large district in the country to adopt a performance pay structure, a controversial system that ties teacher compensation to school performance and teacher evaluations. The Denver Classroom Teachers Association, the union representing 5,700 teachers and other school professionals, said the system in Denver was confusing and unpredictable, leading to high turnover in Colorado’s largest school district. It wanted the district to steer more resources toward base pay instead of incentives.

In the end, the school system agreed to allocate an additional $23 million toward teacher compensation, giving teachers an average salary increase of nearly 12 percent next year. It also overhauled the performance pay system, in some cases increasing incentives for teachers while cutting them for central office administrators.

“We’re very pleased to have reached this agreement that provides our educators with a fair, transparent, and highly competitive salary system,” the school system said in a statement.

Henry Roman, an elementary school teacher who is president of the Denver Classroom Teachers Association, called the agreement “a win, plain and simple: for our students; for our educators; and for our communities.”

“No longer will our students see their education disrupted because their teachers cannot afford to stay in their classrooms,” Roman said in a statement.

Teachers in Denver said they were inspired by their colleagues in other states who walked off the job to protest low pay, deteriorating schools and school funding cuts. Last year, teachers in at least seven states walked off the job in labor actions that ranged from one-day rallies to two-week walkouts that put millions of students out of school.

This year started with teachers in the nation’s second-largest school district, Los Angeles Unified, going on strike to protest funding cuts and the expansion of charter schools. They succeeded in getting the district to agree to hire more teachers to ease overcrowding and to add school psychologists and nurses to treat students.

In 2005, Denver voted to raise property taxes to fund the performance pay program, making the city a trailblazer in incentive pay for teachers. Large urban districts, including New York, Washington and Orlando, followed suit, adopting performance pay plans of their own.

The D.C. performance pay system remains in place, allowing teachers to earn $25,000 in bonuses for performance. But it remains controversial, and critics have recently tied the emphasis on metrics to scandals over falsified graduation rates.

Critics, including teachers unions, say performance pay corrodes collaboration at schools and pushes educators to teach to standardized tests. Supporters say it rewards effective teachers and helps districts hire the best educators for schools that come with greater challenges.

The wave of teacher strikes began a year ago in West Virginia, when educators walked off the job for nine days. From there, educator activism swept into Oklahoma, Kentucky, Arizona and elsewhere.