More than one in 10 pupil absences from primary schools last year was due to an unauthorised family holiday.
The information was revealed in attendance figures just released by the Department of Education (DE).
The proportion of absences due to unauthorised term-time holidays in post-primary schools was much lower at just over 3%.
However, parents of post-primary school pupils were more likely not to give a reason why their child was absent.
Detailed school attendance figures for Northern Ireland are published by the DE every year.
Absences are reported by schools in half-day sessions and recorded as authorised or unauthorised.
In primary schools, slightly more than 5% of all half days were missed in 2017-18, about half a percent more than in 2016-17.
Almost six in 10 pupil absences in primaries were down to illness, by far the biggest reason and recorded as an authorised absence.
However, more than one in 10 absences were down to unauthorised family holidays, while in about 15% of cases no reason was provided for non-attendance.
The proportion of pupil absences definitely due to term-time holidays in primary schools has been rising in recent years.
Five years ago - in 2013-14 - only 7.5% of absences were down to unauthorised family holidays in contrast to 10.3% in 2017-18.
In Northern Ireland, term-time holidays are considered unauthorised absences but there are no fines.
If a pupil's attendance falls below 85% of all days over a period of time, their parents or guardians can be referred to the Education Welfare Service.
Failed legal challenge
Parents who come before the courts for absenteeism are those who have allowed their children to truant over a long period and they can face fines of up to £1,000.
In many parts of England, by contrast, parents can be fined £60 for taking their child on a term-time holiday, with the fine rising to £120 if they do not pay within 21 days.
That previously led to a legal challenge, which ultimately failed.
Term-time holidays appear to be less of a problem in post-primary schools, accounting for slightly more than 3% of absences.
However, no reason was given for about one in every five pupil absences in post-primaries.
The overall absence rate for post-primary schools was 6.7% of all half-days missed, the same as in 2016-17.
Schools in Northern Ireland had higher rates of unauthorised absence than those in England and Wales in 2017-18.