They accused heads of ageism and said schools were reluctant to pay for experienced staff, preferring cheap younger newcomers.
Last year the Government recruited 14,377 people into secondary schools, nearly 5,000 below their target. Primary school recruitment matched the Government's target of 11,500. But the Employment Service says 15,855 unemployed people are claiming the jobseeker's allowance, seeking work as teachers.
Estimates suggest there are as many as 400,000 qualified teachers who have left the profession in recent years.
Yesterday Professor Alan Smithers, director of the Centre for Education and Employment Research at Liverpool University, agreed schools were more likely to appoint young, inexperienced staff because they were cheaper.
Professor Smithers, who is completing a study on the supply of teachers, added: "I have been contacted by a lot of people who want to teach but who cannot get work. Some have good qualifications in subjects such as physics, maths and chemistry, all areas short of teachers."
Ministers are already encouraging people to choose teaching as a second career, as part of a pounds 130m package of measures to tackle the shortfall. They also announced "golden hellos" worth pounds 5,000 for teachers of maths and science.
Ministers hope their Green Paper on the future of teachingwill tempt people into the classroom with salaries of up to pounds 40,000 a year. A new round of cinema adverts, replacing last year's "Nobody Forgets a Good Teacher" campaign, was screened for the first time lastmonth.
A spokesman for the Association of Teachers and Lecturers (ATL) said: "An increasing number of teachers are also on temporary or short-term contracts. ATL has argued for a long time that the best and most experienced teachers ought to be in the classroom."
Steve Jackson, chairman of the pressure group the Association of Teachers Against Ageism, said teachers as young as 31 were being refused work He said: "There is a waste of resources on a terrific scale."
Mr Jackson, a 48-year-old biology teacher, added: "Some people have been made redundant and retrained, others have given up jobs, but it's very difficult to find work, even with a shortage of applicants."
Bob Stonehouse, 50, an experimental chemist made redundant after 22 years with Glaxo, took a post-graduate certificate of education at the London University Institute of Education in 1997 because there was said to be a severe shortage of science teachers.
He applied for dozens of jobs, but was always beaten by younger candidates. The best he has been able to find has been supply cover and one short-term contract last summer.
He said: "The business of science teacher shortages is a myth, because people like me have left good jobs, or turned jobs down to get into teaching, only to find they are unemployable.
"I thought my experience would be valued. But it has become a millstone around my neck.
"I began to realise that the job was always going to the youngest candidates and I do not think it is a coincidence. They are cheaper to employ."
John Dunford, general secretary of the Secondary Heads Association, said: "Most schools appoint the best person for the job. Some people may appear good on paper but they don't seem to be able to get the message across."
A spokesman for the Department for Education and Employment said rules had been changed to allow schools to recoup the full cost of employing experienced teachers from local authorities.
He said that since 1984 people returning to teaching had made up more than half of new recruits to schools.Reuse content