School principals are blaming record-low school attendance rates on cheap air fares tempting families into taking more holidays in term time.

The Education Ministry says only 63 per cent of all school students attended school "regularly" - defined as at least 90 per cent of the half-days - in the second term last year, down from a previous low of 66 per cent in the same term of 2013.

For the first time the Māori attendance rate dropped to just 50 per cent, down from 53.5 per cent in 2013.

Post Primary Teachers Association Secondary Principals' Council head James Morris said the downward trend was concerning because low attendance was linked to lower pass rates in the National Certificate of Educational Achievement (NCEA).

Morris, who is principal of rural Darfield High School in Canterbury, said more parents were taking their children out of school for holidays during term time.

"At our school there are more parents taking students away during term time because flights are cheaper at those times, and flights are cheaper than they used to be," he said.

Nationally, the numbers of students taking at least one half-day holiday during the second term almost doubled from 23,192 in 2015, when the Education Ministry started recording the trend consistently, to 40,729 last year.

The average length of holidays during term time has been more stable, at 9.3 half-days in the second term of 2015 rising only to 9.6 half-days in the same term last year.

But the total amount of time students were absent on "unjustified" holidays increased from 0.4 per cent of the term in 2015 to 0.7 per cent last year.

Absences for an "explained but unjustified" reason have been steady at about 1 per cent of the term in each of the past seven years.

But unjustified absences with no explanation provided, or "truancy", have risen from 1.5 per cent of the term time in 2011 to 2 per cent last year.

"Justified" absences due to sickness also jumped last year, from around 4 per cent of the term in each of the previous six years to 4.6 per cent, due to a rise in "influenza-like illness" last winter.

Regular attendance rates are highest in primary schools and decline as students get older, but have declined over the past seven years at all levels - from 74 per cent to 67 per cent in contributing primary schools, from 74 per cent to 66 per cent in intermediates, and from 63 per cent to 55 per cent in secondary schools.

They have declined most steeply in the poorest communities - down from 57 per cent to 47 per cent in decile 1 schools, compared with a gentler decline from 78 per cent to 72 per cent in decile 10.

Asian students still have the highest regular attendance rate of 73 per cent, but even their attendance is down 7 per cent from 2011.

Attendance has dropped by 6 per cent to 67 per cent for European students, by 9 per cent to 52 per cent for Pasifika and by 6 per cent to 50 per cent for Māori.

Māori and Pasifika students were both absent without explanation (truant) for more than 4 per cent of the term, compared with just under 1 per cent of the term for Asians and Europeans.

However Māori, Pasifika and European students were all absent due to sickness for about 5 per cent of the term. Asian students were sick for only 3.5 per cent of the term.