The tests are set by professionals, pre-tested for cultural bias, agreed to by participating nations, and administered to representative samples of 15-year-olds in each nation. Moreover, the trends over time in average scores are directly comparable, each survey showing whether we are making progress.
So how well did our students do?
In the first Pisa survey in 2000, teachers were congratulated by our minister for students' rock-star performance levels in all subject areas, putting our students in the first three nations in reading and scientific skills and nearly as good in maths.
In the next two surveys, we fared almost as well. But since 2006, we have been in relentless decline in all three subjects, as the impact of that "dumbing-down device", NCEA, began to bite.
As we pointed out in 2013, and predicted again for 2015, New Zealand's average has declined in all three subjects.
Yet NCEA was introduced as a way of raising student achievement levels to world class.
It has achieved the opposite, as we watch our students join the race to the bottom.
The evidence was clear three years ago when we showed that every nation that adopted a policy of standards-based assessment in the senior school and reported their results in school league tables had gone downhill, like New Zealand.
As we predicted, that evidence has not changed.
All five nations that embraced this high-stakes, outcome-driven form of accountability are still well below expectation and seeking answers, while those nations that maintained traditional, norm-based, competitive examination systems have risen or held the line in Pisa.
To illustrate, since 2000, New Zealand students have seen a drop of 42 points in Pisa maths, 20 in reading and 15 in science - a total of 77 points.
Likewise, Australia has dropped by 72 points, as have Sweden (52), United States (33) and Britain (84). None has risen in any subject. Given 15 opportunities to shine, standards-based assessment has failed in every one. Moreover, every state in Australia tells the same story.
These are the only nations in Pisa that have had a clear system of standards-based assessment in place, and allowed league tables, since 2000.
Meanwhile, countries such as Norway, Portugal, Spain, and Poland that rejected this system and league tables have risen steadily in Pisa.
Why blame NCEA? In my view it is the main driver of our students' intellectual efforts in Years 11 to 13.
From 2003 the system fragmented each subject into smaller units from which students picked topics to study. Too often they avoided the hard ones, and chose easier internally assessed options.
Some were less motivated to study because they knew they could have another go if they bombed out. Others stopped working when they had enough credits to pass.
Having no percentages or other finely discriminating grades, top students missed the competition to excel abovethe criteria needed for the highest ofonly four grades.
Some teachers co-operated by coaching students on a narrow range of topics and providing helpful feedback on trial questions to ensure a better outcome in the forthcoming tests and projects that they themselves would set and mark.
Those are some of the reasons. Some schools praise NCEA, especially if they see more weak students gain a qualification in an overly indulgent system. But what is the worth of a qualification that only misleads a future employer or tertiary institution?
Strangely enough, our Government described the latest Pisa results as "pleasing". When will our politicians accept strong independent evidence?
