The academic achievement of millions of American students faltered during the pandemic — and in many cases, has not recovered three years later. The latest data on student attendance offers one explanation: Far more students are missing many days of school compared with before the pandemic.

Nearly 70 percent of the highest poverty schools experienced widespread, chronic absenteeism in the 2021-22 school year, compared with 25 percent before the pandemic, according to a new analysis released on Friday by Attendance Works, a nonprofit that aims to reduce chronic absenteeism, and the Everyone Graduates Center at Johns Hopkins University, which focuses on high school graduation preparedness.

In these schools, about a third or more of the student body was considered chronically absent, defined as missing at least 10 percent of the school year, or about two days of school every month. That includes all absences, including sick days and school-imposed suspensions.

“Prior to the pandemic, going to school every day was still the norm,” even in the poorest schools, said Hedy Chang, the executive director of Attendance Works. That is no longer the case.

In the most affluent schools, widespread chronic absenteeism also increased: to 14 percent of schools, up from 3 percent before the pandemic.

Those numbers are from the 2021-22 school year. Is it possible it simply took more time for students to get back into a routine?