When it comes to studying absenteeism, almost all research has focused on students who miss a full day of school, not a class here and there. But skipped classes are responsible for a startling number of unexcused absences among middle- and high-school students, according to a recent study in the journal AERA Open.

“Part-day absenteeism in secondary school is extremely prevalent,” said Jing Liu, a PhD candidate in economics of education at Stanford’s Graduate School of Education and co-author of the report. “In fact, it explains more classes missed by students than full-day absenteeism does.”

Liu and Camille Whitney, MA/PhD ’15, tracked class-by-class attendance for more than 50,000 middle and high school students in an urban district over five years.

“If we consider absence at a class level instead of a daily level, 52 percent of all absences from classes are on part days rather than full days,” said Liu.

When only full-day absences were counted, the average rate of chronic absenteeism in their data was 9 percent across all grades. (Students are considered chronically absent if they miss more than 10 percent of their classes, Liu noted.) “After incorporating part-day absences,” he said, “the rate jumped to 24 percent.”

What’s more, 92 percent of the part-day absences were unexcused, compared with slightly more than half of the full-day absences.

Students were most likely to skip the first and last periods of the day. The researchers also saw a sharp increase in unexcused absences, both full- and part-day, in the transition year from middle school to high school—but while these full-day absences declined in subsequent years, unexcused missed classes continued to increase through 12^th grade.

Putting the research into action

The study suggests that schools may need to explore different policies and practices to address absenteeism. The district Whitney and Liu studied, for example, recently implemented a new online attendance-tracking system to improve the way both part- and full-day absences are counted.

School officials are also using the data to pursue interventions, such as family conferences and home visits, to help reduce chronic absenteeism.

Liu discusses the findings further in the video below.