Only 13% of children are getting the recommended amount of exercise, according to a new study.
Researchers say more homework may be having a negative impact on the take-up rates.
The all-island study involved some 6,600 students across the Republic of Ireland and Northern Ireland.
It shows just 17% primary school students and 10% post primary pupils were getting at least 60 minutes of moderate-to-vigorous physical activity every day.
These figures are down from the 19% and 12% recorded nine years ago.
Researchers say the increased volume of homework may be having an impact.
Since 2010, children at both primary and post-primary level are spending more time on homework, increasing by 13 and 17 minutes respectively.
Around six in 10 students were spending no more than two hours in front of a screen.
Students in 6th year were most likely to go over this screen time guideline.
However, since 2010 there has been a 7% rise in the number of primary school children playing community sport at least four times a week.
More than half of them were also taking part in PE classes at least twice a week, compared to 41% in 2010.