Carol Fitz-Gibbon, professor of education at Durham University, was due to address the first conference of OFSTIN (the self-styled Office for Standards in Inspection) - a band of retired headteachers and academics who challenge OFSTED's methods.
Professor Fitz-gibbon argues that there are grave doubts about whether the lessons observed by OFSTED inspectors can be said to be typical of that teacher or school.
"The entire design seems to be based on received wisdom rather than checked by proper methods . . . using methods of the last century . . . is as unadvisable in social science as it would be in medicine."
Much of her thesis is based on a survey of 108 heads, of whom 61 had undergone an inspection. It found that most had little faith in the reliability of inspectors' judgments, though newer heads were more positive because, Professor Fitz-Gibbon suggests, an inspection can bolster the head's authority.
She raised concerns about the cost, concluding that "there are numerous instances coming to our attention of inspection acting as a poison in the system". She has called for an independent inquiry into OFSTED, saying it is currently "an embarrassment to anyone who understands social science".
The conference will decide today on OFSTIN's next move. On Thursday, delegates were due to hear summaries of evidence for and against OFSTED garnered from teachers, inspectors, governors, parents and union representatives.
OFSTIN, which has mischievously adopted OFSTED's typeface for its publications, along with the motto Quis custodiet ipsos custodes? has had financial support from the National Association of Head Teachers and "a substantial cheque" from the Secondary Heads Association.