Just about every teacher, parent and student who endured the sad and dragged-out mess of online learning during the COVID-19 pandemic understands that it was a disservice to young people.

It hurt them academically and emotionally, and whatever was gained from a public health standpoint wasn’t fairly balanced against all that was lost.

That evidence, plain as it is, remains anecdotal and personal. But a crucial study this month from the Center for Education Policy Research at Harvard University gives us a scientific sense of who was hurt most by the wrongheaded decisions to lock the schoolhouse doors and keep them locked for months on end.

The exhaustive study reviewed testing data from 2.1 million students in some 10,000 schools in 49 states, including Texas.

Its conclusions are a must-read as we look back on the decisions of our politicians, public health authorities and teachers unions that kids should stay home.

“High-poverty schools were more likely to go remote, and they suffered larger declines (in learning) when they did so,” the study’s authors note.

Meanwhile, Black and Hispanic students were much more likely to be placed in remote learning and were kept in remote learning for longer periods of time during the 2020-21 school year.

The rate of learning decline in schools became steeper for all income groups the longer schools remained remote. But the decline was far more precipitous for high- and mid-poverty schools. This was especially true in math, but also true in reading.

We are thankful to say that the study demonstrated that Texas was among the group of states that abandoned remote learning for all income levels the quickest. Our students almost surely benefited from that.

Of course, Texas did not have powerful local teacher unions demanding that schools stay closed until every manner of social ill unrelated to public health was addressed. Keep in mind that the Chicago Teachers Union infamously tweeted that efforts to reopen schools were “rooted in sexism, racism and misogyny.”

While urban unions dug in against helping kids get back into the classroom, and even left-leaning governments were helpless to reopen their schools, learning losses mounted.

According to the study, “high-poverty schools spent about 5.5 more weeks in remote instruction during 2020-21 than low- and mid-poverty schools.”

Now, we see a widening of the racial learning gap in schools across America. That gap “happened because of negative shocks to schools attended by disadvantaged students, not because of differential impacts within schools,” the study notes.

That is unconscionable, and its effect could ripple through a generation. Let’s remember it the next time someone tries to put the lock on the schoolhouse door.

The Dallas Morning News editorial board. Visit dallasnews.com.