The surprise resignation of Minneapolis Superintendent Bernadeia Johnson has placed the district squarely among a growing number of troubled urban school systems that have lost their top leaders recently.

"We are going through a period at the moment where we are seeing substantial turnover," said Michael Casserly, the executive director at the Council of Great City Schools. "It's not clear if it is episodic or if there is a larger trend beginning to emerge."

Los Angeles; Seattle; Albuquerque, N.M., and now Minneapolis are just a few of the districts that have lost their top executive this year.

Education experts say the departures are part of a larger national trend where superintendents are getting increasingly bogged down by complex political landscapes and well-oiled resistance inside and outside of the district.

Former Minneapolis Mayor R.T. Rybak defended Johnson on his Facebook page Tuesday, saying that when he was mayor he always said he had the "second toughest job in town."

"People care a lot about potholes, but they care a whole lot more about their kids," said Rybak, now the executive director of Generation Next, which is working to improve student achievement.

Minneapolis has churned through 14 interim and permanent superintendents in the past 30 years. The average tenure for superintendents nationally is just 3.2 years, according to a 2014 study conducted by Casserly's organization.

"I don't know of many other places, other than the National Football League or police chiefs, where the turnover is as high as it is in urban school systems," Casserly said.

Johnson resigned Tuesday citing the need to spend more time with her elderly grandparents. She said the next phase of work at the district required "a level of intensity and focus to which I am unable to fully commit at this time."

She was not available for an interview Wednesday.

'Angry and upset'

Johnson joins a growing number of newly departed school leaders in large urban districts. In Los Angeles, the superintendent resigned in October after a disastrous rollout of a $1.3 billion iPad program and a court case that struck down teacher tenure. Albuquerque's superintendent resigned in August after the board hired an attorney to look into a "serious personnel issue" that was never disclosed.

In Minneapolis, Johnson had been the superintendent for four years, the longest tenure in at least a decade.

Rybak said Johnson was able to act with a sense of urgency and built strong support from the school board and community organizations.

"In many ways she was the most successful politician in Minneapolis in the last decade," Rybak said.

This school year, Johnson had just implemented her strategic academic plan, which called for ambitious reductions in the achievement gap. The district was about to begin a new school funding model where the schools with the most needs would receive bigger budgets. She also imposed moratoriums and closer scrutiny on suspensions of students of color.

But recent data showed the district's achievement gap in math and reading scores was at its highest level in at least four years. Johnson also endured growing scrutiny from community organizations that said she was not addressing the needs of students of color.

During a November board meeting, Johnson expressed vivid frustration with the lack of academic progress for students of color.

Breaking from her prepared statements, Johnson said she gets so "angry and upset" that some of the smartest people in the state work in Minneapolis, but the district hasn't figured out how to make academic progress for certain student groups.

"We have to let go of the things that we are stuck with … if they are not effective," she said.

Rep. Carlos Mariani, DFL-St. Paul, director of the Minnesota Minority Education Partnership, said when he first met with Johnson, she was the one who brought up the district's troubling disparities in discipline. Black students, particularly males, were getting suspended at rates nearly 10 times higher than white students.

Mariani said Johnson told him she didn't have the political capital to force change on her own, so she needed him to pressure her publicly.

"She said, 'I'm dealing with some pretty strong institutional behaviors here. I need to point to others from the outside asking for change,' " Mariani said. "I love that because it showed she was playing an inside and outside game. That can be very effective."

Richard Mammen, the district's outgoing board chair, said many employees in Minneapolis have a "this too shall pass" mentality regarding the regular turnover of district leaders.

"The thought is that the leader that is there today may not be there tomorrow," Mammen said. "That gets in the way of innovation."

Casserly said not every district, even those with high turnover, faces institutional resistance. People will rally behind strong leaders, Casserly said. "It's up to the leader to get everyone on the same page," he said.

Casserly said the impact of extremely high turnover in a school district is universal.

"The reforms and improvements can get undermined by changing leadership," he said. "It can sometimes have a real effect on the overall stability."

Alejandra Matos • 612-673-4028