Students in the United States could see their lifelong earnings cut by an average of 6% to 9% unless schools are able to make up for learning losses incurred during the pandemic, a Stanford University professor warned on Thursday.

Hanushek’s remarks came during the Massachusetts Institute of Technology’s Covid-19 Challenges and Opportunities in K-12 Education summit.

“But we do know is that there is a growing cost over time of remote learning and the hybrid systems we have and the lack of actual in-class teaching as we knew it in 2019,” Hanushek said.

In August 2020, Eric Hanushek estimated that students from first grade through 12th grade would, on average, lose about 3% of their previously predicted lifelong earnings. That was if all schools returned to normal in September.

Of course, they didn’t. Now, he estimates that it will average to be between 6% and 9% — though that average doesn’t reflect how kids with less money and fewer resources will likely suffer more.

Hanushek compared the pandemic to other historical moments where students were out of normal schooling for long periods of time.

Students during Argentina’s school strikes or post-war Germany suffered economic losses that marked them decades later, he said.

That spells serious problems for the United States’ gross domestic product. In August 2020, Hanushek predicted that GDP would be 1.5% lower on average every year for the rest of the 21st century.

Now, he estimates that it will be 3% to 4% percent lower for the rest of the century.

That can’t be remedied by returning to 2019 education methods whenever the pandemic ends, he warned. Instead, America’s education system has to make up for the learning loss.