Gerard Kelly’s polemical editorial, “Pisa is not perfect but rankings are here to stay” (26 July), failed to inform readers that for more than 150 days, Pisa failed to provide any rebuttal of the conceptual (not technical) flaw in the Rasch model.

Mr Kelly’s bizarre suggestion that the UK government should continue to use scarce taxpayers’ funds to prop up Andreas Schleicher’s empire will not fool those who have sought a full methodological debate within the international research community on the validity of inferences drawn from Pisa rankings.

The grandeur of Pisa has toppled. Amid the rubble, if only Mr Kelly had looked, are approaches to pedagogy that owe more to rhetoric and ideology than careful research and scholarship.

The first results from the OECD’s Teaching and Learning International Survey (Talis) advocate a pedagogy that has at its core the notion that students must be enabled to construct meaning for themselves. However, the world’s largest education experiment - Project Follow Through in the US, which monitored the attainment of low-income children for 20 years from the late 1960s - identified the teaching methods advocated by Talis as locking disadvantaged children into a life of poverty.

Talis misconstrues the predicate “learn” exactly as Rasch misconstrues “ability”. Without a robust challenge concerning Pisa’s Rasch-generated plausible values, we risk a future OECD blueprint for “world-class teaching” that could damage the life chances of disadvantaged children across the world.

Stephen Elliott, Retired researcher, Antrim, Northern Ireland.