After waiting in the wings for months, the National Education Association endorsed Joe Biden in the Democratic presidential primary on Saturday night — a move that will likely translate to significant volunteer and financial support for the former vice president. 

The NEA is the country’s largest teachers union and largest labor union, with some 3 million members.

“Biden is the tireless advocate for public education and is the partner that students and educators need now,” the NEA’s president, Lily Eskelsen García, said in a statement. “With so much at stake in this election, educators are determined to use their voice to propel Joe Biden to the White House.”

The decision reflects the significant narrowing of the Democratic field, and Biden’s frontrunner status after winning a string of state primaries. Eskelsen García said earlier this year that the NEA would wait to back a candidate until it saw who could deliver votes.  

Before landing the NEA’s endorsement, Biden had attracted fewer high-profile endorsements from local teachers unions than Sen. Bernie Sanders, though the American Federation of Teachers, the country’s second-largest teachers union, had encouraged its members to support Biden, Sanders, or Sen. Elizabeth Warren before she dropped out. Earlier this year, Biden also lagged behind Sanders and Warren in donations from individual teachers.

The choice came far later than it did last presidential election cycle. During the 2016 election, the NEA endorsed Hilary Clinton in October 2015 — angering some educators who said the NEA didn’t give enough consideration to Sanders, her challenger. That prompted changes in the endorsement process for both the NEA and the AFT.

In her justification for the NEA’s endorsement, Eskelsen García pointed to Biden’s promises to raise teacher pay, increase school funding, and hire a secretary of education who has experience as a public educator. The union also pointed to Biden’s plans to “address racial injustice,” raise special education funding, and expand access to pre-kindergarten — though those are all positions that Sanders also holds.

The NEA said Biden “uniquely understands” the work of education support professionals, noting that he was once a school bus driver, and highlighted the work of his wife, Jill Biden, a longtime educator and NEA member. 

In response to Eskelsen García’s announcement on Twitter, some educators said they didn’t feel they’d had enough say in the decision, and said they supported Sanders.

The NEA hasn’t spent any money in the presidential race yet, but has significant resources at its disposal.During the 2016 presidential election, the NEA’s super PAC spent just under a quarter million dollars to support Clinton’s campaign, federal campaign finance records show. It also donated $1 million to Priorities USA Action, the main super PAC that backed Clinton.