The president of the nation’s second-largest teachers union is calling for full-time in-person school this fall, a move that could smooth the way back after a year where teachers often resisted a return to classrooms.

“There is no doubt: Schools must be open. In person. Five days a week,” Randi Weingarten, president of the American Federation of Teachers, said in a speech Thursday delivered via YouTube and other streaming services. “Given current circumstances, nothing should stand in the way of fully reopening our public schools this fall and keeping them open.”

Weingarten has long said that she wants school to operate with teachers and students physically present, though many of her union’s members have resisted. Her call was greeted with skepticism by some who see unions as having been overly cautious or outright obstinate.

Union leaders have generally said schools cannot open in a pandemic unless it is safe, and the school year has been marked by endless disputes over what is required for safety.

But with the Biden administration pushing hard for a full return to classrooms, and with coronavirus vaccinations widely available and districts across the country promising weary parents they will reopen fully this fall, it appears that opinion among teachers is shifting. The largest teachers union in the country, the National Education Association, suggested Thursday that it agrees with the AFT.

“NEA supports school buildings being open to students for in-person instruction in the fall,” said a statement from NEA President Becky Pringle. She did not specify whether that would be five days a week, but a spokeswoman later said NEA does support a full-time return to in-person learning.

In her statement, Pringle also suggested unions were responsible for making sure schools open safely. “Educators will continue to lead in making sure each school has what it needs to fully re-open in a safe and just way and to ensure the resources exist to meet the academic, social and emotional needs of all students,” the statement said.

Many school districts have offered students at least part-time options this spring, with very few still completely remote. Many districts are using hybrid systems, in which students are in the building only a day or two a week, or where in-person learning is not available to all students. Federal data show that as of March, nearly half of schools were not yet open full time for all students.

Districts in the South and Midwest were much more likely to be fully in-person than those in the Northeast and West. And students of color were more likely to be attending remotely than White students.

Nonetheless, districts across the country have promised that they will reopen full time this fall, and Weingarten’s speech suggests her local chapters will not try to fight that.

“We have been planning for fully reopening in the fall for months,” said Michael Casserly, executive director of the Council of the Great City Schools, which represents urban districts. “We welcome the unions in the ongoing planning.”

Weingarten, who is close to the White House, also puts her union more fully in line with President Biden, who has pushed for schools to reopen. Asked about the union leader’s comments, White House press secretary Jen Psaki replied, “We agree.”

Weingarten said Thursday that her union will run a $5 million “back-to-school for everyone” campaign this summer to persuade teachers and families to return. “The United States will not be fully back until we are fully back in school. And my union is all in,” she said.

Weingarten announced that the AFT executive council had endorsed her call for a return to school, as well as a vision for how to improve education as the system begins to recover from the pandemic. Nonetheless, some of her members may resist.

One teacher addressed Weingarten on the AFT Facebook page: “Last I knew, the pandemic did not magically disappear. Please do not speak for the rank and file who love our union but who are NOT `all in’ for returning to five days a week.”

In her speech, Weingarten defended previous union resistance to going back to classrooms this year, accusing critics of scapegoating and vilifying teachers and blaming them for “problems outside their control.” But she said conditions have changed since then.

Keri Rodrigues, president of the National Parents Union, a group that often opposes teachers unions, supports full reopening but gives AFT little credit for making it happen.

“Teachers unions have fought science every step of the way on the grass-roots level,” she said. “I think Randi is reacting to the fact that she is well aware that parents and families are tired of the endless uncertainty about whether or not schools are going to reopen five days a week next year and have made it clear that if they do not, they will be seeking other options.”

Weingarten said that a return to in-person school is “not risk free” but that those risks can be managed with vaccination and other mitigation measures, including the use of masks and maintaining three feet of distance between students. She said new federal money can help schools implement a variety of protective measures.

Vaccination has been the game changer, she said. The union’s data show that 89 percent of its members are fully vaccinated or want to be. And she noted that the Pfizer-BioNTech coronavirus vaccine has been authorized for use in children ages 12 to 15.

She called on districts to reduce class sizes — something teachers have long supported — to maintain three feet of distance, as the Centers for Disease Control and Prevention recommends. She suggests that school systems work this summer to find more space to keep classes smaller.