This study looked at 7,798 teenagers aged 16 to 19 in one county in western Norway. They reported their own sleep, and this was matched to official school records of their grade point average (GPA). It was a snapshot in time, so it cannot show that sleep causes grades to change.
Every sleep measure was tied to higher odds of being in the lowest quarter for grades, and the pattern was graded, so worse sleep went with worse odds. Teenagers who slept 7 to 9 hours had the best average grades (4.0), while those sleeping under 5 hours had lower grades (3.5) and more than three times the odds of poor performance. Very late bedtimes were worse, but so were bedtimes before 22:00. A bigger gap between weekday and weekend bedtimes also went with lower grades.
Adjusting for age, gender and family background did not weaken these links, and for some measures the odds rose slightly. Missing school explained part of the pattern, but all sleep measures stayed significant.
The authors suggest that earlier and more regular bedtimes across the week may be useful targets for teenagers, and that sleep is worth checking when a student is struggling at school.
The numbers Stats and what the terms mean
The statistics behind the plain-language claims above.
- Hysing, 2016: sleeping under 5 hours and odds of poor grades, OR 3.54.
What the terms mean:
- OR (odds ratio) compares the odds of an outcome between two groups. 1 means no difference, above 1 means higher odds, and below 1 means lower odds.
Source: Hysing M, Harvey A, Linton S, et al.. Sleep and academic performance in later adolescence: results from a large population‐based study. Journal of Sleep Research (2016). doi:10.1111/jsr.12373