In this June 14, 2012, file photo, Los Angeles Unified School District Superintendent John E. Deasy tours a school in Los Angeles. Deasy, a former Prince George’s County superintendent, announced his resignation this week. (Damian Dovarganes/AP)

Los Angeles Unified School District Superintendent John E. Deasy — a former school superintendent in Prince George’s County — resigned last week as head of the nation’s second-largest school district, ending a tumultuous tenure that included battles with the teachers union and rifts with the school board.

Deasy took the helm of the 640,000-student system in 2011, quickly becoming known for his education-reform efforts and his take-charge attitude in working to turn around the troubled district. Ramon Cortines, 82, who ran the Los Angeles schools before Deasy, has agreed to return from retirement this week and lead the school system on an interim basis until a permanent successor is named.

U.S. Secretary of Education Arne Duncan expressed “disappointment” that Deasy was resigning from “one of the nation’s toughest school systems to manage.” In a statement, Duncan lauded Deasy for his accomplishments in the past 31 / 2 years, including overseeing higher graduation rates, fewer student suspensions and “a record number” of students taking Advanced Placement classes.

Deasy has “an unwavering commitment to doing what’s right for kids, and I am hopeful that the next superintendent of LAUSD can continue to build on the progress that the district has seen under John’s leadership,” Duncan said. “We simply cannot afford to see improvements in student achievement slow down or stall in the nation’s second-largest school district.”

Deasy is among a cadre of urban school leaders that has been pushing urgent change, much of it disquieting to teachers unions and moderate school officials, who say large public institutions need time to make adjustments. His official biography, which was still on the LAUSD Web site Friday, says that “he is a man on a mission.”

Deasy has connections to two of the largest philanthropies driving public-school change across the country. He was a fellow in 2006 at the Broad Academy, a program to groom leaders of urban school districts and state education agencies. It is funded by Eli Broad, the California billionaire whose foundation promotes charter schools, technology in the classroom and pay-for-performance for teachers.

Deasy served as superintendent of the Prince George’s school system for two years, abruptly leaving Maryland’s second-largest district in 2008 to join the Bill and Melinda Gates Foundation as deputy director for K-12 education. The Gates Foundation is an influential proponent of data and technology use in the classroom as well as the idea that good teaching can be measured and should be rewarded.

In 2010, Los Angeles hired Deasy as its deputy superintendent, a decision that ultimately led to his promotion to the top job.

“I am overwhelmed with pride in what this administration has accomplished for the youth of Los Angeles over the last four-plus years,” Deasy wrote in his resignation letter, which he delivered Wednesday. “Every day we have remained focused on our mission, about which we are crystal clear: we lift youth out of poverty.”

There were significant gains in academic achievement under Deasy. But his tenure was fraught with contention: teachers complaining of being alienated, board members criticizing his leadership style and others worrying about two controversies involving technology.

An investigation is underway into the fairness of the bidding process for a $1.3 billion program to provide every student and teacher in the school system with an iPad. Deasy said he looks forward to the inspector general’s review and said the investigation will “determine that there were no missteps on my part in the process whatsoever.”

Deasy said he hopes the school board moves forward with the project. “If it’s dead, we’re doomed,” Deasy said during a recent interview on NPR.

This year, a $130 million software program that was designed to track students’ information encountered problems during its rollout, making it impossible for teachers to input grades or know which classes students were supposed to be enrolled in.

Deasy was a proponent of holding teachers accountable for test scores and recently testified against the teachers union in a lawsuit over teachers’ job protections.

He also was criticized by teachers and school board members for what they said was an autocratic leadership style. He defended his approach during the NPR interview, saying that he placed students’ rights first and that “it made some adults uncomfortable.”

United Teachers Los Angeles said that Deasy’s departure “is an opportunity to move in the direction of fully-funded schools and collaborative management, instead of treating school improvement as a ‘corporate turnaround’ model, over-emphasizing testing, undermining equity and access for students, and attacking educators.”