(NewsNation) — It’s back-to-school time, but is your child on the bus? Students across the country have been absent at record rates, and it’s keeping some children from making the grade.

A recent report from Stanford University shows more than a quarter of students missed at least 10% of school during the 2021-2022 school year, compared to just 15% before the pandemic.

The study found roughly 6.5 million more students were “chronically absent,” meaning they missed at least 18 days of school. An estimated 240,000 of those students in 21 states are unaccounted for — they just went missing.

“We really don’t know what happened to those students,” said Yvonne Johnson, president of the National PTA. “I wouldn’t say they’re dropping out. I would say it’s more we’ve lost track of them because of the pandemic.”

The chronic absences couldn’t come at a worse time. COVID restrictions hit students hard, which forced many out of school and saw them relegated to virtual classroom instruction. It was difficult for many students who benefit from direct student-teacher interaction. In rural communities, poor computers and unreliable Wi-Fi compounded the problems.

According to the National Education Association, however, chronic absenteeism is not exactly a new phenomenon. Persistent issues such as unsafe schools, housing instability, illness and unreliable transportation contributed to chronic absenteeism long before the coronavirus.

“It is a trickle-down effect that when students do not come to school, it affects everything,” said Johnson. “It affects how they do in school, it affects graduation rates, it affects the funding that they get. And so absenteeism is not a new issue, it’s just gotten worse since the pandemic.”

The result?

Many children are at least one grade level behind in one or more subjects and struggling to catch up. Experts say interventions like engaging with families, strengthening student-teacher relations, school health services and free student meals could help.

“We cannot continue to have this kind of absenteeism in school,” said Johnson. “The bottom line is that if a child doesn’t come to school, they cannot learn. So the goal is to make sure that kids are actually returning to school buildings that are coming to school every day.”