Professor Ian Menter of Glasgow University has warned of "a shadow of doubt" over the Executive's target of employing 53,000 teachers by 2007.
His comments followed the publication last week by the Headteachers'
Association of Scotland of a survey suggesting that teacher shortages were a national rather than a local problem, that shortages existed across all secondary subjects, that supply cover had become a serious problem in some areas and that a few schools were having to skew the curriculum.
Professor Menter, who was appointed to the new chair in teacher education at the university's curriculum studies department at the end of last year, said: "The Scottish Executive is having to face two major challenges in recruiting and retaining teachers.
"The first is to ensure that there is a match between the overall demand for teachers and the available supply. This is particularly challenging at present because of the attempts to reduce class size for maths and English and because of the reductions in class contact hours brought in following the McCrone settlement.
"The second is to ensure that there is a sufficient pool of supply teachers available for temporary cover. They need to be in the right places and with the right specialisms. The study which we carried out for the Executive last year found there were indeed major difficulties in some areas and some subjects.
"While Mr Peacock may be justified in claiming that in Scotland teaching is viewed as a relatively attractive profession, we did nevertheless find many supply teachers in our study who felt they were not well supported and that their contribution was not fully recognised."