A more accurate count of the number of school leavers shows NCEA achievement rates are not as high as previously thought.
The National Certificate of Education Achievement was introduced in 2002.
The Ministry of Education is counting leavers it previously missed, such as those in alternative education or who unsuccessfully move between schools.
The figures are more accurate, but show the proportion of school leavers with NCEA qualifications is lower than thought.
For example, 69% of last year's school leavers had Level 2 of the NCEA - a benchmark schools thought they had passed in 2008.
The Secondary Principals Association says the figures are disappointing.
Education Minister Anne Tolley says they show that too many students are leaving school without the minimum qualification needed to succeed in today's world.