Of course, when countries such as Scotland appear to be performing badly in such tests, it is difficult to be credible when crying foul. Criticism is best directed when performance is improving. None the less the weaknesses inherent in international comparisons are overdue for exposure, not least because apparently conclusive research is not the exact science it often seems.
This is why the warnings by Ann Kitchen from Manchester University (page one) about the Third International Mathematics and Science Study are significant. Her work does not imply Scottish pupils can rest on their laurels. But it does suggest that knee-jerk reactions are unwise when there can be the most basic linguistic confusion in test questions between "cents" and "per cent".