Andreas Schleicher's defence of Pisa is welcome as it enables several accepted myths to be publicly aired.
Mr Schleicher states that "any assessment ... will have some uncertainty". Practitioners, researchers and academics in the field are all aware of this. However, hasn't he forgotten to explain this to the politicians? Students and teachers in many countries are suffering from restricted, test-based curricula because ministers are basing their policy on the Pisa metric.
He also relates the astonishing fact that the way in which teachers and schools teach topics varies. Even a newly qualified teacher would find that condescending. The blustering continues with the assertion that Pisa will provide "robust comparisons of the performance of education systems in ways that reflect any remaining uncertainty". No, sorry, Mr Schleicher: that is called good teaching and learning based on sound classroom assessment, differentiated teaching and the sensitive development of learner autonomy. That is where our education budget should be focused, not on fanciful comparisons designed to feed the lucrative test-development industry.
Professor Bill Boyle, Chair of educational assessment, University of Manchester.