Seven out of 10 older school children in Ireland do not get enough daily physical activity.
A study published in The Lancet Child and Adolescent Health Journal also found inactivity is more common in girls than boys.
It found that 71% of Irish 11-to-17 year olds get insufficient physical activity every day, with some 63.5% of boys deemed to be insufficiently active, rising to 80.5% among girls.
The World Health Organisation recommends young people get at least one hour of physical activity a day.
Niall Moyna, Professor of Health and Human Performance at DCU, wants all primary schools to take physical education seriously.
Mr Moyna said: "I think there needs to be a dedicated physical education teacher in every primary school, that's where kids learn their behaviours.
"A lot of kids get to secondary school and they don't have the fundamental motor skills, so it's like coming to secondary school not having learned basic arithmetic and asking them to learn algebra, it's a similar analogy."