Problem solving scores edged up from the 16-24 age group to peak at those aged 25-34, before steadily dropping.
"People improve these skills [literacy and numeracy] over time through being in tertiary education and employment," a report based on the OECD results and released tonight found.
"Lower average skill levels in older age groups may be due to different school and life experiences, the effects of advancing age or a combination of both."
Minister for Tertiary Education Skills and Employment Steven Joyce said the OECD results were good news for New Zealand, with its ranking for adult literacy improving to fourth from 12th in 1996.
However, numeracy results have remained unchanged since 2006 and are less impressive.
"The results show that our system is on the right track. In the years ahead we will focus particularly on lifting numeracy skills further, while seeking to maintain our strong performance in literacy and problem-solving," Mr Joyce said.
Survey reports were last published by the OECD in 1996 and 2006. The key findings of this year's report are:
LITERACY
The average literacy score of a New Zealand adult was below only Japan, Finland and the Netherlands. It wasn't significantly different from Australia and Sweden.
Adults with high literacy skills make up 16 per cent of New Zealanders, compared to 12 per cent of adults who have low literacy skills.
This split is comparable to Australia and better than countries including England and the US, that have a higher proportion of people with low literacy skills.
New Zealand is one of the few countries where literacy scores increased significantly since 1996.
NUMERACY
New Zealand's average numeracy score of 271 was in the middle of OECD nations, above Australia but behind 12 other countries.
More Kiwis have low numeracy skills (19 per cent) than high numeracy skills (15 per cent).
Adult numeracy skills have remained unchanged since 2006.
Men scored significantly higher on average in numeracy than women, with an average score of 278 to 265. There was no difference on average in literacy and problem solving skills.
The differences between ethnic groups are greatest in numeracy. That contrasts with problem solving, where the average scores for Maori and Pasifika are closer to those of New Zealand Europeans.
English-speaking, foreign-born immigrants to New Zealand scored higher in literacy and numeracy than English-speaking, native-born New Zealanders.
PROBLEM SOLVING
This skill was tested for the first time.
New Zealand's average score for problem solving using technology like a computer was fifth highest in the OECD, behind Japan, Finland, Australia and Sweden.
