Elementary school students in the U.S. ended the school year four to five months behind their expected level of academic achievement, according to a new report.

Why it matters: Months of school closures and often inferior remote education eroded what schoolchildren would have learned since the pandemic began, and caused some to go backwards.

• The effects of pandemic-driven learning loss will weigh on the economy for decades ahead, and could worsen if schools can't reopen normally in the fall.

By the numbers: Researchers from McKinsey compared academic achievement for K-12 students after the 2020-21 school year to matched students from previous years, and found that students were testing 10 points behind in math and 9 points behind in reading on average.

• The numbers were worse for historically disadvantaged students — students in majority Black schools ended the year with six months of unfinished learning, while students from low-income schools finished seven months behind.

The big picture: The authors wrote that "unless steps are taken to address unfinished learning, today’s students may earn $49,000 to $61,000 less over their lifetime owing to the impact of the pandemic on their schooling."

• That translates to an impact on the U.S. economy of $128 billion to $188 billion every year as these students enter the workforce.

Between the lines: More time spent in remote education correlated to worse outcomes — students in more urban schools fell further behind students at rural schools, which returned to in-person education faster.

What to watch: How successful efforts to close the learning gap over the summer prove to be, and whether schools can reopen for full-time in-person education even as the Delta variant — and lagging vaccination rates — cause COVID-19 case numbers to rise.