When they spoke in December, Randi Weingarten, president of the American Federation of Teachers and a longtime Democratic operative, had a pointed message for Rochelle Walensky, then the incoming director of the CDC: The administration had one chance to get the guidance for school openings right.

“The last CDC director so messed this up and so undermined the credibility of the CDC that you really have one shot to get this right and to be a credible scientist leading the CDC,” Weingarten said she told Walensky.

When the CDC released its highly anticipated guidance in mid-February, Weingarten was pleased with parts and disappointed with others. She thought, for instance, there should have been more emphasis on coronavirus testing in schools and on proper ventilation. But she said she appreciated the science-based blueprint and was eager to promote the agency’s work…

In the end, the guidelines may have slowed down school openings more than sped them up. The document recommended that communities with high levels of virus transmission operate school remotely or on a part-time schedule — known as hybrid — with reduced numbers of students in the building at any given time. Under the CDC’s rubric, that included the vast majority of the country.