White House Chief of Staff Ron Klain said Tuesday that most schools had not made the proper investments to ensure that it was safe for students to return to the classroom.

Klain told CNN’s Erin Burnett that the primary issue was money and that some schools were not able to reopen yet because they had not been able to make the necessary adjustments recommended by health officials.

Burnett quoted Democratic Colorado Governor Jared Polis as saying that schools were the safest place to be — a position that has been supported by a number of studies and even the CDC — and asked Klain why so many public schools were still closed.

“I will give you a word, money. That’s why the President of the United States sent a plan to Congress even before they took office to make the investments to make the school safe,” Klain said.

He argued that one study was based on a group of rural schools that had used a private grant to implement a series of safety measures — which included dramatic reductions in class size.

“Governors who made the investments, Governor Polis is a great leader in this field, he’s done a lot, but in other states we haven’t seen those kinds of investments,” Klain continued. “President Biden sent a plan to Congress to make sure the majority of schools can be open within 100 days. We need Congress to pass that plan to do the kinds of things you need to do so that the schools can be safe, so the teachers can be safe, so the students can be safe. Sadly, it costs money.”

“No. That’s definitely true. But we have all seen of course that the transmission is just not happening,” Burnett pushed back, noting that a number of teachers unions had balked at the last minute, staying closed when they had planned to reopen.

“Ron, why do you think that the unions, in many cases, are overruling what studies show?” Burnett asked.

“I don’t think unions are overruling studies,” Klain replied, arguing that the schools were choosing to stay closed because they hadn’t yet taken the proper precautions. “I think what you’re seeing is schools that haven’t made the investments to keep students safe, again, Wisconsin study were classrooms of 12 on average. That requires a lot more classrooms, a lot more teachers, or you know other kinds of arrangements to get them small.”

“We need to do things to open safely. Most teachers I talk to want to be back in the classroom. They just want to know it is safe,” Klain concluded. “We as a country should make the investments to make it safe.”