Joseph G. Allen is an associate professor and director of the Healthy Buildings program at Harvard University’s T.H. Chan School of Public Health. Helen Jenkins is an associate professor of biostatistics at Boston University School of Public Health.

For an entire year, parents, teachers and superintendents have waited for evidence-based guidance from the federal government on how schools could navigate the pandemic. It has finally arrived. The updated guidance for schools that the Centers for Disease Control and Prevention released on Friday gives schools the road map they need to fully reopen.

The journey to this revised document has been long and bumpy. When the CDC first issued its guidance for schools to reopen on Feb. 12, it had all sorts of problems.

As we laid out at the time, the report had two major flaws. The first was that it relied on overly strict community spread metrics. At the time of its release, 90 percent of the country’s school districts were in communities with the highest level of spread (denoted by the color red), and the CDC essentially said middle and high schools in those districts should stay remote while elementary schools should remain in hybrid mode. This was despite many studies showing within-school transmission could be controlled with good mitigation in place, regardless of community spread. To get to the “blue” level, the lowest of the CDC’s four-color system, communities would have to reach 1 case per 100,000 per day. That won’t happen this calendar year. In fact, we might never hit that level of spread with this virus. Ever.

The second big issue was the continued reliance on six feet of distancing for students. By last fall, there was evidence that three feet of distancing was sufficient to keep risk low in schools, when other control measures were in place. But in the Feb. 12 guidance, the CDC held firm on six feet in schools, even though the practical implication was that kids would never fully go back to in-person learning due to space restrictions.

The Feb. 12 report had other relatively minor issues, too: Ventilation wasn’t highlighted enough. All sports, including outdoors, were banned for schools at the “red” level, which doesn’t make sense. Physical barriers and “sneeze guards” were recommended, even though they are useless in the face of aerosol transmission. It also emphasized intensive cleaning, which we also now know is a waste of effort and resources.

The new guidance addresses all of this. The biggest change is the adoption of three feet of distancing for students as sufficient when all other prevention strategies are in place, including universal masking, hand-washing and enhanced ventilation. The CDC also added some other good caveats: When community spread is high and cohorting not possible, the CDC urges that middle and high schoolers revert to six feet. It also emphasizes times when masks cannot be worn and therefore the six-foot rule is needed, such as during lunch. (One of the best strategies we’ve seen for managing lunchtime is to have only half the school use the lunchroom each day, while the other students eat in their classes. Teachers can put on a movie to reduce talking, which keeps emissions low. And, of course, open the windows!)

The CDC also provided important tweaks on its community spread metrics. Now, it says that higher community spread could lead to in-school transmission, “if layered prevention strategies are not in use.” In other words, if schools have good controls, they can be open regardless of community spread. That’s a big change, and one that matches the science.

The report also now includes a full section on ventilation, with the guidance in line with what we have been saying for months: Schools should be bringing in more outside air and upgrading their filters. The report also dropped the recommendation to use plexiglass barriers, which can actually impede airflow. Cleaning is still overemphasized, unfortunately.

The CDC also corrected its guidance on sports, too. It now says outdoor sports are fine, though it still recommends maintaining six-feet distancing, which we think is not necessary during outdoor youth sports when athletes wear masks. Still, it’s a move in the right direction. We should be actively encouraging all outdoor sports.

Finally, the agency kept the critical sections on equity, testing and contact tracing, which were quite good in the first version.

There’s no sugarcoating it: The first report on schools from CDC was off. That was issued in the third week of the Biden administration. To its credit, the administration didn’t waste time or double down in a defensive crouch. They listened to scientists and updated the guidance.

The road map is clear for how to get kids back in class. To any school that’s closed and meets these measures, it’s time to open. To any school that opened without any of these controls in place, they must be implemented immediately. There can be no more delay.

Read more: