Education leaders are blaming changes to University Entrance (UE) for an unexpectedly big drop in the number of teenagers gaining the qualification.
Government figures show only 58 percent of last year's Year 13 students gained UE, down from 70.6 percent in 2013; 20,578 people gained UE last year, down from 24,940 in 2013.
The fall follows the Qualifications Authority's decision in 2011 to make UE harder by matching it with NCEA Level 3.
That raised the number of level 3 credits required for UE this year from 42 to 60, with a further 20 credits required from either Level 3 or Level 2.
The number of credits required from a list of approved subjects has also increased, from 14 credits in each of two subjects from a list of approved subjects to 14 credits in each of three subjects. Students must also have 10 level one credits proving their numeracy and 10 level two credits proving their literacy.
At the time it announced the change, the Qualifications Authority said it did not expect much of a fall in the number of school leavers with UE. It said only 5 percent of students who achieved UE did not also reach NCEA level 3, and that was mostly because of the subjects they had studied.
But Universities New Zealand chairperson Harlene Hayne said the fall in the pass rate was higher than expected.
She said a decrease was expected because UE had been made more difficult, but it was not clear why so many students had fallen short.
"We did some estimates last year and certainly the number was higher than expected, but again assuming that all of the students were very well aware of the changes, I'm not sure what else we can make of the very high number of students who didn't make the cut."
She said universities supported the changes to UE.
Post Primary Teachers' Association president Angela Roberts said the changes were expected to result in a drop of only about 5 percent in the UE pass rate.
The big drop was likely due to the increased number of credits required from the list of approved subjects, she said. Some students might have stuck with subjects they enjoyed which were not on the approved list and gambled on getting enough credits in other subjects.
"So kids are being punished for making decisions about what they're interested in rather than jumping through the bureaucratic hoops that universities have driven."
Wellington Girls' College principal Julia Davidson said six or seven of the school's students who were expected to get UE missed out.
"The change that has affected them has been not getting the 14 credits in each of the three university-approved subjects."
Victoria University vice-chancellor Grant Guilford said the number of applications from students who narrowly missed out on UE had doubled and the university was working with about 175 who would have achieved UE under the old system.
He said there was no single area in which the students had fallen short.
"It appears that the changes to the university entrance requirements, that have been quite well signalled, haven't been picked up for some reason, and some of these students are turning up at our door just not quite with the requisite requirements even though many of them are academically capable individuals."
Professor Guilford said many of the students would still be able to attend university this year but some would first have to complete extra courses with their previous school or at the university.
Education Minister Hekia Parata said some students might have been caught out, even though the change was announced three years ago.
UE had been set at the level of learning students needed to reach in order to be successful at university, she said.
The Government's provisional figures show achievement rates for Level 1 of the NCEA remained unchanged last year at 82.6 percent of Year 11 students, Level 2 increased slightly to 86.8 percent of Year 12s, but achievement of Level 3 dropped to 78.6 percent of Year 13s.