Results reflect our poor investment
In world rankings, Wales did well on science but turned in below-average performances on reading and maths. The much-touted media comparisons with Eastern European countries were absolutely right - our performances were close to Croatia and Azerbaijan.
It is the reason why we did so poorly that is the key. The Pisa studies cannot tell us whether Wales did poorly because of our high levels of social deprivation, the usual excuse for failure trotted out by some Welsh heads and teacher unions in their explanations of the results.
But Northern Ireland and Scotland have similar levels of deprivation to us in Wales and their results were better and closer to England's. And a word in praise of England - its high levels of migrants with poor language skills, deprived communities in places like Sheffield and Leeds that have no Welsh parallel and its large number of poorly performing schools at the "bottom", as it were, again without Welsh parallel, suggests it may have understated strength in its schools.
To be well ahead of us in Wales, given these factors, deserves some praise.
But saying that all our Welsh failure is down to our schools is not correct. Our science results are our best area of performance, yet science is the most school-influenced of all three subjects studied, since most families don't do science with their children in the way they do reading or maths. How can our schools be doing well in science and not in other areas? This is unclear.
Two things stand out as likely educational explanations for our problems though.
First, we do poorly mostly because we have an absence of high-performing children, which suggests that our schools may have responded to the taunts that they fail the less able by over-compensating and lavishing attention on them to the neglect of the historically advantaged Welsh able children. In this, they may have been encouraged by the Assembly government's focus on "lifting the floor" through the basic skills agenda rather than "raising the ceiling" of the able.
Alternatively, some of the emphasis upon the gifted and talented that is present in England might have had an effect.
Second, it is clear that the chickens may finally be coming home to roost for the Assembly government as a result of its manifest inability to passport increased public expenditure into education in the way so evident in England and Scotland.
In the science part of Pisa, heads in Wales and other countries were asked about the adequacy and availability of resources such as IT and instructional materials like books and schemes. The Welsh heads were more likely to report inadequate provision than the heads across the world.
If countries with Third World levels of provision were stripped out, then no doubt Wales would be even more inadequate than the remaining First World countries.
Professor David Reynolds lives in South Wales and is professor of education at the University of Plymouth.