Almost 30,000 registered teachers are staying away from the classroom despite staff shortages in Scottish schools, the BBC has learned.
Thousands of teachers are not applying for school jobs
Over the past few months schools have reported serious problems filling vacancies with children being sent home due to lack of teaching cover.
The General Teaching Council (GTC) is to survey probationary teachers to discover why they are failing to apply.
Discipline problems and too few permanent posts could be to blame.
In some cases teaching unions have reported members having to take up to three classes at a time while councils, including Dumfries and Galloway, have had some posts going unfilled for months.
The GTC said 55,000 staff are in schools on any given day but half as many again are not in work.
A spokesman added that although 30,000 registered teachers are not in teaching posts this could be due to a variety of reasons, including career breaks, illness and caring for children.
He added that the figure could also include retired teachers who continue paying their registration to enable them to be kept up-to-date with the profession.
Matthew MacIver, chief executive of the GTC, told BBC Scotland: "This is the highest number of registered teachers we have had in Scotland since 1982."
He said he hoped the survey of probationary teachers would help discover why they were not in permanent posts following their induction year.
"I'm beginning to question where all these probationary teachers are," he said. "We hear so much about shortages of teachers, especially supply teachers.
"I think it's time we had a really good look to see where the probationary teachers are going."
Former Glasgow teacher Phil Grahame said teachers may be put off by a lack of permanent contracts and unruly pupils.
He said: "I think we have to offer people permanent contracts even if that involves over-staffing because that will take up the slack of people who go off sick through stress and other problems.
"A lot of people leave the teaching profession because of the stressful nature of dealing with young people."
He pointed out that many people can feel intimidated by groups of youths on the streets, but teachers were faced with them in the classroom every day.
Mr Grahame said: "As a teacher you have to do something with them, make them biddable and get on with their work.
"Some people aren't good at that and the stress gets to them and eventually they leave."
The Scottish National Party has called for an immediate inquiry into the number of teachers failing to apply for jobs.
The party's education spokeswoman Fiona Hyslop said: "The Scottish Executive's flagship policy to cut class sizes in S1 and S2 will never be achievable if 30,000 of Scotland's teachers are not teaching in our schools.
"There will always be teachers who opt out of teaching, for example, to have families, but if more than half of registered teachers are not teaching we have a problem.
"As recently as last spring, the first minister was saying the problem was not as serious as teachers were making out. This is obviously not the case."
An executive spokeswoman said: "There will always be people who for whatever reason want to do something else.
"There could be personal circumstances. A large number of female teachers take career breaks to have children."
Education convenor at the council umbrella body Cosla Ewan Aitken said: "In the bad old days when money was tight we did try to save money by offering short contracts but only one or two authorities do that now.
"We realise we have to make posts attractive to staff."