The signatories include Professor Antony Flew, Professor Ted Wragg, of Exeter University, and Professor Carol Fitz-Gibbon, director of the Curriculum Evaluation and Management Centre at Newcastle University, who organised the letter. They say the financial and human costs of OFSTED inspections, and their consequences for schools, “demand that the processes of inspection are subjected to scrutiny at least as rigorous as those which OFSTED claims, on no objective evidence, to be following”.

They are worried about comparability of judgments made by different inspectors. The academics (and one OFSTED-registered inspector) say credibility should be established by:

* showing that the sampling of pupils, teachers and lessons is sufficiently representative to support the judgments;

* demonstrating whether different inspectors make consistent judgments when observing the same person and events;

* demonstrating the validity of the judgments made - for instance, by showing that a lesson rated “good” has led to effective learning. In other words, explains Professor Fitz-Gibbon, inspectors’ prejudices about teaching methods should not be able to influence their judgments about the quality of the lesson. “OFSTED needs to be reformed root and branch,” she said. Their work demanded a far higher reliability than academic research “because they’re dealing with people’s lives”.

Professor David Reynolds of Newcastle University, another signatory, wanted to ensure OFSTED methods “are above reproach”. The letter is also signed by Professor Tony Edwards, of Newcastle University, registered inspector Dr Reed Gamble, and Professor Tim Brighouse, chief education officer of Birmingham.

A spokeswoman said OFSTED would respond in full later.