The national scholastic examination NCEA had a difficult birth.

Despite a long gestation it arrived without coherent standards or any incentive for students to achieve better than average, and because most of the marking was to be done by the class teacher rather than externally there were concerns at how nationally consistent results could be assured.

Most of those deficiencies appear to have been fixed over the 10 years that NCEA has been in schools.

So it comes as a surprise that Auckland Grammar School has decided to largely abandon NCEA at the first level of senior examinations this year, and that two other schools, St Peter's College and Macleans College, are said to be considering a similar step if Auckland Grammar can get away with it.

That is the first question to be answered. The Education Ministry points out that the law requires all state schools to make NCEA available to pupils who want it.

Grammar's principal John Morris says the NCEA will continue to be available for students who request it, but he expects nearly all of his 550 Year 11 students to opt for the Cambridge international examination instead.

Many schools already offer that exam as an extra challenge for capable students, but not to the near-exclusion of NCEA.

The larger question is, should Auckland Grammar get away with it? That is probably the dilemma facing Education Minister Anne Tolley, who has been reluctant to comment. Should a school be allowed to opt out of the national examination system?

Diversity and choice in education are desirable. State schools would be better if they were given much more autonomy in their employment, remuneration, enrolment and fee-setting policies. In cities they should be able to compete for pupils by emphasising different parts of the curriculum and promoting different values.

But they and their pupils need to be measured against a clear and consistent national standard. Indeed, the more diversity is permitted in the operation of schools the greater the need for a national check on their standards and for a system of credits that pupils can easily carry from one school to another.

Grammar's principal has publicly opposed the NCEA since its conception, but he has not previously challenged the need for a national examination.

His objection to the NCEA also seems to have changed slightly. At the beginning he questioned its standards, methods and rigour. Now he has found its regime of constant internal assessment does not suit the learning style and nature of most boys.

He may be right that most boys would prefer an end-of-year examination to an unrelenting schedule of tests through the year but clearly the day when NCEA can be considered a soft option has passed. A glance at its papers can usually dispel that notion.

The questions involve research rather than rote learning. They reflect a curriculum that aims to encourage inquiry and discovery rather than the transmission of accepted wisdom.

If this system does not suit the teaching style of Auckland Grammar School, that is rather sad. But it would be sadder if such a prestigious school's decision - made public on Sunday just as NCEA results were about to be posted online - detracted from a sense of achievement for thousands of young people this week.

Other principals have been quick to defend the NCEA, attesting to its demands on pupils and the effort most of them maintain throughout the year. It is not perfect and should constantly be improved but it is now the nation's recognised educational credential.

Auckland Grammar should think again.