United Teachers of Dade President Karen Aronowitz is announcing Monday that she will not seek a fourth term at the helm of the union, which represents some 21,000 teachers and 11,000 other school employees in Miami-Dade.

Deciding that “eight years in office is long enough,” Aronowitz is clearing the way for a new leader to take over in February.

“I’m proud of what we have done together: the way we restored democracy and financial stability to the union; what we have accomplished for members; and the promotion of our belief in what this union can accomplish as we move forward,” Aronowitz wrote in a letter to teachers and employees.

Her departure will mark the biggest change in the union’s leadership since the fall of union boss Pat Tornillo. He ran the union for four decades until a Miami Herald investigation revealed he financed a lavish lifestyle with union dues and a federal prosecution put him in prison.

Aronowitz was the first president elected after Tornillo. During her term, the union has treaded rocky waters: rebuilding trust among members after Tornillo’s abuse; bargaining during the recession; and representing teachers through massive changes in public education, like merit pay and charter expansion.

“I hope that I have really been the bridge between some ugliness in the past and what will be the future,” Aronowitz told The Miami Herald. “I think when people look back, they will say, ‘She was firm through the whole thing, she was able to keep the ship afloat.’ ”

Aronowitz plans to return to teaching English and to stay involved in education policy as a vice president with the American Federation of Teachers.

Several teachers said Aronowitz’s greatest accomplishment was working with the Miami-Dade district to ensure no full-time teachers were laid off during the recession. Teaching jobs were budget casualties in Broward and elsewhere.

“That’s one of the best things she could have done,” said Brian Peterson, a local education observer.

Teacher Marta Laura Zayas said Aronowitz has fared well with a difficult task, but had room for improvement.

“She’s a strong leader, however in the area of public relations and particularly in addressing the Hispanic membership she may have found better ways to reach out to them,” Zayas said.

Aronowitz highlighted several accomplishments, like successful political organizing. “I’m most proud of turning our members into activists and finding forceful, new leadership,” she said.

Her decision to step down, which she said she made a long time ago, leaves the union’s top job wide open. Nominations for candidates are due Dec. 7 and at least two current leaders plan to compete for president: Secretary-Treasurer, Fedrick Ingram and First Vice President Artie Leichner. Teacher Eugenio “Geno” Perez, who ran against Aronowitz in 2010 and has challenged those elections, is also mulling a run.

Aronowitz has endorsed Ingram, who grew up in Liberty City and Overtown, was named Miami-Dade teacher of the year in 2006 and has served on her team. Ingram said he wants to advocate for teachers and build stronger ties to the community.

“I’m willing and ready to stand in the gap for those teachers who do that hard work every day,” he said.

Leichner is organizing a slate of candidates, dubbed the UTD Progressive Caucus. In an email, he said running was the only way to improve the “malaise and fear” he sees among teachers and change the “almost unilateral decision-making that has come to characterize how things are being done at UTD.”

The candidates will face an increasingly frustrated work force. Teachers have grappled with changes from the state Legislature, like evaluations driven by student test scores. More recent frustration has stemmed from teachers who feel the union should fight harder for them. A new contract gave instructors the first raises in several years and lifted the starting salary. But thousands of mid-career teachers saw annual increases of about $300. Last week, teachers were angry to learn the Miami-Dade School Board lifted salary caps for district administrators by 10 percent to 30 percent.

The union is also struggling internally, with some employees who oppose Aronowitz’s leadership holding “Occupy”-style protests outside UTD headquarters. Some have won legal challenges against the online voting process.

David Kirsner, a union steward at Coral Gables Senior High who supports Leichner, said, “You might say that it’s a very splintered union at this stage in the game.”