(NewsNation) — Irregular sleep and late bedtimes could lead to lower grades and more behavioral problems at school among teenagers, a new study out of Stony Brook University suggests.

The study, funded by the National Institutes of Health and published in the journal Sleep, analyzed data from about 800 children taking part in a larger study. Participants wore a device that recorded their movements for a week, allowing researchers to study the students’ sleep patterns.

Those with bedtimes that tended to vary had an increased chance of receiving a D or lower during the previous grading period, compared to students who went to bed at more consistent times.

Participants who went to bed later, awoke later, or had varying numbers of hours of sleep per night received fewer As, the study found. Students were also more likely to be suspended or expelled in the previous two years if they woke up later, varied the number of hours they slept per night or varied when they went to bed each night.

The study’s authors suggested that later bedtimes could result in students arriving late to school, affecting both their learning and behavior.

The researchers also noted that many adolescents are “biologically inclined to later hours, which conflict with early school start times,” according to a news release.