There is no research evidence over the past 30 years to support Mr Osler's thesis, according to Dr Brian Boyd, associate director of the Quality in Education Centre at Strathclyde University and a former secondary headteacher.
Dr Boyd argues that the move towards setting, outlined last week at the launch of the Inspectorate's report on class organisation, will bring selection and a return to the "qualy" one step closer.
In a letter to The TES Scotland, Dr Boyd complains that Mr Osler and the Inspectorate have joined the English agenda "by proposing a simplistic and dogmatic solution to what is a complex problem".
Underachievement is a problem common to most advanced European countries and cannot be solved by setting in English and mathematics within the 5-14 levels, Dr Boyd maintains.
"What game is being played here?" he asks. "Has the Inspectorate bought into a right-wing elitist agenda and seeks to justify it by saying that teachers find mixed-ability too difficult to manage? What teachers find difficult to manage is the plethora of new initiatives, the refusal by the Scottish Office Education and Industry Department to let one initiative bed down before promoting another one, and the continual emphasis on things that can be measured."
Dr Boyd goes on to state that there is growing evidence that underachievement is best tackled by improved motivation, self-concept and "emotional intelligence".