More than 36,000 children skipped classes to take holidays during a single school term last year.
Education Ministry figures show 5.7 percent of the 630,000 students covered by its attendance survey last year missed an average of one week in the second school term last year.
The report said holidays during term time accounted for 0.6 percent of all class time, an increase of 0.2 percentage points from 2015.
That represented about 36,000 surveyed students with at least one half-day of holiday during Term 2 in 2016, it said. The holidays averaged 9.5 half-days - or nearly a full week of school.
Asian students had the highest percentage of time spent on holiday during term time, followed by Middle Eastern, Latin American and African students, then Pākehā students.
Principals Federation president Whetu Cormick said he was surprised so many children had taken a holiday in a single school term.
"The occasional day here or there isn't harmful, but when children are away for long periods of time, that is a concern for schools," he said.
Mr Cormick said some families were late returning their children to school after holidays or took them out of school early.
"Sometimes families do need to take time outside the normal school holidays because their own employment situation doesn't allow them to take holidays when the children do," he said.
Association of Intermediate and Middle Schools president Sharon Keen said the figures were higher than she would have expected, possibly because of the time of year they were collected.
"The last week of Term 2 is when we often do lose children to overseas travel. I guess that's people travelling to a warmer climate in the middle of our winter."
Ms Keen said trips could be educational.
"We prefer people to avoid term time, but we also have to realise that sometimes, a trip - the learning experiences - can be quite valuable as well," she said.
Ms Keen said families usually arranged for school work to take with them if their child was going to miss a lot of school time.
"We've had a child who travelled through Europe and had weekly contact with her class and reported on what she'd seen, and wrote about her experiences. Poetry, all sorts of things. That was probably, in the big picture of her life, a very valuable experience."
Canterbury West Coast Secondary Principals Association president Phil Holstein said families were asked to seek permission before taking children on holiday, but that did not always happen.
He said some simply informed the school their child would be absent and others asked permission, though they had already purchased tickets.
"But I think that's important, at least the parents have informed the school," he said.
Mr Holstein said his school, Burnside High School, was emphasising attendance this year because it was so important for children to be at school.
"We really believe that attendance and punctuality at school are the first steps in succeeding at school," he said.
Secondary Principals Association president Mike Williams said some trips were educational, but children were still missing out on school.
"There's going to be a cost, and I suppose that's the point we have to make to parents. This might be an amazing educational experience for your kids but there will be a cost in terms of their learning in other areas," he said.
Mr Williams said research showed attendance was strongly linked to achievement.
"It is a problem. We know we've got good evidence, good data, that attendance is critical," he said.
Lower achievement link - but never too late
Education Ministry senior staffer Katrina Casey said it did not support taking students out of school during term-time for holidays.
"There is an increasing body of evidence that shows time out of class results in lower achievement," she said.
"For example, a Year 11 student who only turns up at school half of the time has just a one-in-five chance of getting NCEA Level 1. A student who attends every day has about a 90 percent chance of achieving that qualification."
Schools and parents were best placed to make judgements about in-term holidays, Ms Casey said, but they were formally regarded as an unjustified absence.
"Holidays in term time were previously categorised as justified absences as schools deemed them to be satisfactorily explained when they received notification of the holiday from caregivers. They are now categorised as unjustified absences and a parent's note does not provide justification."
The ministry's report said 74.5 percent of students at decile 10 schools attended regularly in Term 2 last year, compared to 52.9 percent at decile 1 schools.
It said 2.9 percent of arrivals to class at decile 1 schools were late compared with 0.8 percent at decile 10 schools.
The report said South Island regions had above-average attendance, while North Island results were mixed. Te Tai Tokerau had the lowest figure at 55.9 percent. Wellington had the highest percentage of lateness to class at 1.6 percent of classes.
It said there was a strong relationship between attendance and achievement of NCEA Level 1 - but it was never too late to improve a student's chances. "Attendance in Year 11, out of all years from Years 7 to 11, had the largest effect on the probability of a student achieving NCEA Level 1," the report said.