A study involving 845 secondary school students has revealed that each hour per day spent watching TV, using the internet or playing computer games at average age 14.5 years was associated with poorer GCSE grades at age 16. Additionally, each hour of daily homework and reading was linked to significantly better grades. Surprisingly, however, the amount of physical activity had no effect on academic performance.
Median screen time was four hours a day, of which around half was spent watching TV; median sedentary non-screen time (reading/homework) was 1.5 hours.
Each hour per day of time spent in front of the TV or computer in Year 10 was associated with 9.3 fewer GCSE points in Year 11 — the equivalent to two grades in one subject or one grade in each of two subjects. Two hours was therefore associated with 18 fewer points at GCSE, and the median of four hours, with a worrying 36 fewer points.
The burning question: are some screens better than others? Comparison of the different screen activities revealed that TV viewing was the most detrimental to grades.
More positively, each hour of daily homework and reading was associated with an average 23.1 more GCSE points. This was a U-shaped function, however, with pupils doing over four hours of reading or homework a day performing less well than their peers. But the number of pupils in this category was relatively low (only 52 pupils) and may include students who were struggling at school.
The benefits from spending time on homework or reading were not simply a consequence of spending less time staring at a screen; screen time and time spent reading or doing homework were independently associated with academic performance.
Do note that, although some homework was doubtless done on the computer, this was not counted as screen time for the purposes of this study.
The finding of no significant association between moderate to vigorous physical activity and academic performance is more surprising, given the evidence for the benefits of exercise and physical fitness for cognition. The median was 39 minutes of moderate to vigorous physical activity a day, with a quarter of the students getting less than 20 minutes a day, and a quarter getting more than 65 minutes.
The data used was from the ROOTS study, a large longitudinal study assessing health and wellbeing during adolescence. Objective levels of activity and time spent sitting were assessed through a combination of heart rate and movement sensing. Screen time, time spent doing homework, and reading for pleasure, relied on self-report. Medians were used rather than means, because of the degree of skew in the data.
 . Revising on the run or studying on the sofa: prospective associations between physical activity, sedentary behaviour, and exam results in British adolescents. International Journal of Behavioral Nutrition and Physical Activity [Internet]. 2015 ;12(1):1 - 8. Available from: http://link.springer.com/article/10.1186/s12966-015-0269-2