New York City Mayor Bill de Blasio, who has helped steer the nation’s largest school district, will seek the Democratic nomination for president, he announced Thursday.

De Blasio, in his second term, is known for pushing universal prekindergarten in his city, championing a controversial school turnaround program, and selecting a schools chief who has backed a divisive effort to diversify the district’s selective high schools.

He joins a crowded field of Democratic primary candidates who’ve already started speaking out about education issues.

De Blasio’s announcement video touted his drive to offer universal prekindergarten, starting with the city’s 4-year-olds. With support from the state, the city used a multi-year plan to convert existing half-day seats to full-day, to create new prekindergarten centers around the city, and to partner with community-based organizations to offer more seats. In 2017, he announced a similar rolling effort for 3-year-olds, starting in two low-income neighborhoods.

The mayor is also known for a $773 million Renewal initiative, recently ended after three years, that was designed to turnaround some of the city’s struggling schools. The idea was to offer intensive supports and avoid closing schools.

“Though some of the nearly 100 low-performing public schools have shown better results, many have fallen short of the improvements that Mr. de Blasio predicted,” the New York Times reported in February.

De Blasio and schools Chancellor Richard Carranza have championed a divisive plan to increase black and Latino enrollment in the city’s elite exam schools by eliminating an entrance exam they say favors families with the resources to prepare their children to excel on the test. Instead, de Blasio wants to offer seats to the top students at each of the city’s middle schools.

A single standardized test can never capture the talent of young people. We need a fairer way to admit students to our Specialized High Schools. pic.twitter.com/B0pPz2zNq3

— Mayor Bill de Blasio (@NYCMayor) June 4, 2018

De Blasio has already taken on an issue that’s generated some concerns for other candidates: charter schools. He clashed with high-profile charter school leaders over co-locating charter schools in buildings with regular, district-run schools. Charter supporters have said there is an unfair funding gap between traditional schools and charter schools, with facilities needs presenting a significant financial burden.

Photo: Mayor Bill de Blasio speaks during a news conference on June 21, 2017 in New York. --Bebeto Matthews/AP