Chris Woodhead quoted some damning extracts from the report by Dr James Tooley in a recent New Statesman article, fuelling speculation that the document was about to be released.
But, last week, the Office for Standards in Education said that no publication date had been fixed.
"I don't believe Dr Tooley was late with his first draft - due in January - but any manuscript of this kind has to go through a series of drafts," an OFSTED official said.
Dr Tooley, newly appointed to a chair at Newcastle University, has been scrutinising papers published in academic journals.
He has measured their "usefulness" but has also been looking for examples of political bias.
It is this aspect of the study which has attracted particular criticism because Dr Tooley is seen as a right-winger.
He believes that the school-leaving age should be reduced to 14 and has also said that IQ tests could replace some exams.