Students who average more study hours do better in school. But a study published last week in the journal Child Development shows that students who stay awake to study more than their average – i.e., to cram – up their odds of failing a test or having difficulty understanding instruction the next day.

To allay fears of correlation not implying causation and all the myriad other factors that could confound a study like this (perhaps students who cram are the same students most likely to do poorly in school?), the UCLA researchers Gillen-O'Neil, Huynh, and Fuligni had 535 students keep track of their sleep time, study time and academic problems for 14-day spans in 9th, 10th and 12th grades. The longitudinal data of these student "diaries" allowed the team to ask how individual students performed on days after average sleep/study, compared to the same student's performance on days after which the student had traded sleep for study.

Interestingly, they found that in 9th grade, there was no penalty for cramming. In 10th grade, staying awake to study started to predict higher next-day hits for the responses "did not understand something taught in class" and "did poorly on a test, quiz, or homework." And by 12th grade, kids who traded sleep for study showed a marked spike in academic problems the day after cramming.

The researchers offer a nifty explanation for the bloom of the cramming penalty across high school. See, kids get overall more sleep as freshmen than they do as seniors – from 7.6 hours per night in 9th, to 7.3 hours per night in 10th, to 7.0 hours per night in 11th, and finally 6.9 hours per night in 12th grade. It's as if a freshman's generally adequate sleep can absorb one night's cramming, but a senior, who is already getting more than 2 hours less than the 9 hours of sleep recommended by the National Sleep Foundation, is hypersensitive to any additional reduction. As your grade goes up and your sleep goes down, the penalty for staying up to study gets stiffer and stiffer.

Jamming facts into the adolescent brain at the expense of sleep is exactly counterproductive.

So if you're a student, don't cram. And if you're a parent, don't let your kid cram. And with that I think I heard even through cyberspace the great collective guffaw of impossibility. How can a high-schooler not cram? Dude, it's like part of the high school code of conduct!

The researchers suggest distributing study time evenly throughout the week (and with that, another guffaw...). They also point out that teenagers work, socialize and watch TV – and that rather than these extracurriculars shrinking to absorb extra time spent cramming, it's sleep that suffers.

If your teenager wants to do well on tomorrow's test, perhaps he or she could short screen time rather than sleep time?

You know the excuse: "But Dad [pronounced 'DaaAAaad'], I have to see if Katniss and Peeta survive the Games! And then I'll just stay up a little bit to finish studying!" Well, that excuse has now been shown to be scientifically invalid.