Superintendent William R. Hite, Jr., left, greets students as they enter the new Barack Obama Elementary School in Upper Marlboro. (Mark Gail)

William R. Hite Jr., the Prince George’s County school superintendent, announced Friday that he will leave his post as head of the Washington region’s third-largest school system to run the Philadelphia school district.

Hite, who has worked in the county for six years, was one of two finalists in a nationwide search to replace Arlene Ackerman. He is expected to leave the 123,000-student system later this year for one of the largest school systems in the nation.

Pedro A. Ramos, chairman of the Philadelphia school reform commission, said: “Today we take a giant step toward providing safe, high-quality educational opportunities for all Philadelphia children. Dr. Hite is an eminent educator and a proven transformative leader.”

The departure of Hite, 51, is certain to create upheaval in Prince George’s, which has had rapid turnover at the helm.

He leaves a school system that has made significant strides, including improvements on state test scores and the implementation of successful educational reforms. But the school system continues to lag behind many others in the region, and it faces dwindling enrollment, a continued lack of trust in the public schools and an increase in the number of students from low- income families.

“I’m happy with the progress we’ve made,” Hite said. “I just wanted every single student in Prince George’s to have an opportunity. And I think overall the quality of the education that the students are receiving now is better than it was a couple of years ago.”

Hite said the Philadelphia job is a “tremendous opportunity” to make an “even greater impact in a larger system.”

In a statement, the county school board said “it was with deep disappointment that we greet the news” of his departure.

“He has led Prince George’s County schools with vision and innovation under financial challenges that might have broken a weaker superintendent,” the board said.

With Hite’s departure, the Board of Education finds itself in familiar territory: scrambling to find a replacement for a departing superintendent.

It happened in 2003, in 2005 and again in 2008.

This time, there is no natural successor. This month, Bonita Coleman-Potter, deputy superintendent, resigned to take a position in Mississippi.

“At this point, we’re looking at what the transition could look like,” board Chairman Verjeana M. Jacobs (District 5) said.

Residents and community leaders said they are once again concerned about the lack of stability in the system.

“Montgomery County had Jerry Weast for [12] years, and we can’t keep a superintendent for five years over here,” said Howard Stone, a former school board member and a strong supporter of Hite. “It just doesn’t send a good signal to have a change so often at the head of the school system.”

Five superintendents, including Hite, have run the school system in a permanent or acting capacity since 1999. Hite has one of the longest tenures of the five. He joined the county in June 2006 as deputy superintendent. He took over as interim chief of the school system after the abrupt resignation of John E. Deasy in 2008.

County Executive Rushern L. Baker III (D) and County Council Chairman Andrea Harrison (D-Springdale) said in a joint statement that they valued the “extraordinary contribution” Hite has made to the school system and that their desire was for him to stay and continue his work.

Hite will remain in Prince George’s for 120 days.

Under his county contract, he was required to give the board 120 days written notice. If Hite did not give notice, he would have had to forfeit his severance benefit.

The 120-day notice requirement was included in Hite’s four-year contract after the abrupt departure of Deasy. It was designed to help the school system have a smooth transition, Jacobs said.

“I’ve always been committed to making sure there is a transition process,” Hite said.

He said he wanted to “make sure this school system doesn’t miss a beat at the beginning of the school year.”

Jacobs also said Hite could recommend someone from his administration to serve in a temporary capacity. The board will name an interim superintendent in coming weeks.

“One of the things I’ve been able to do is form an effective leadership team that is focused on the work, not the people,” Hite said. “When you have a team like that, even if the parts changes, the focus doesn’t. We have talented folks on my senior team who could run the system . . . and carry it forward.”

R. Owen Johnson Jr., a former board member who hired Hite, said residents should be proud that two of the top educational leaders in the county were lured by other districts.

“It’s a credit to what has been done here,” he said.

Hite, who had two decades of educational experience in Virginia and Georgia when he came to Prince George’s, was hired in May 2006 to serve as Deasy’s deputy superintendent.

In that role, he helped shape much of Deasy’s agenda. Hite became interim superintendent in late 2008, stepping into the top post as the county slashed the school budget because of the economy. He signed a four-year contract in June 2009.

Since then, scores on state tests in Prince George’s have improved. Hite’s main focus has been on education equity, trying to ensure that students throughout the county have the tools needed to graduate from high school, ready to go to college or go to work.

After Deasy left, he continued to improve student achievement and implemented numerous initiatives, including an information technology high school, a student-run bank at Parkdale High School and a middle college program that allows high school students to obtain their diploma and associate degree in four years.

“We need consistency,” said Theresa Saunders, the outgoing president of the Prince George’s County Parent Teachers Association. “It’s important for our youth to continue to achieve, and it would be good to see the momentum to continue.”

The decision to hire Hite signaled a desire for stability in a system that has suffered from a revolving door of superintendents.

School chiefs over the past decade have left because of political challenges, including conflicts with school board members, state senators and delegates, and other elected officials.

In 2002, the school board fired former superintendent Iris T. Metts after political infighting.

The state legislature stepped in and dissolved the county’s elected board and created an appointed board (which has since been replaced with another elected board). Andre J. Hornsby was hired, then resigned after a corruption scandal, which lead to his imprisonment.

Howard Burnett became acting superintendent after Hornsby’s departure while the board began a national search. It hired Deasy in 2006. He stayed for two and a half years and took a position with the Bill and Melinda Gates Foundation.