Thousands of newly qualified teachers quit the profession because they find dealing with unruly pupils too difficult.
Ofsted chief inspector Sir Michael Wilshaw blamed this on a woeful lack of training which left new teachers 'floundering'.
And as a result 40 per cent had left teaching within five years of qualifying.
Sir Michael claimed teachers were being tutored by people with little 'up-to-date' experience and senior staff did nothing to support them.
About 30,000 teachers are trained each year, suggesting that some 12,000 of those switch careers after a short period of time. The average cost of training is around £10,000 – meaning tens of millions of taxpayers' money is being squandered annually.
Sir Michael said: "How many times have heads said to me their trainees had been tutored by people with little or no up-to-date school experience or a record of outstanding teaching?
"Trainees have been sent into schools inadequately prepared to deal with poor behaviour. Even worse, how many times have I heard they were left to flounder because they received little or no support from senior and middle leaders?"
He added: "I think most of them leave because of misbehaviour. They find it far too challenging, far too difficult."
Speaking at an education conference in Nottingham, Sir Michael said from September inspectors will ask newly qualified teachers if they 'well supported, particularly in dealing with pupil behaviour'.
If they were struggling, Ofsted will check who trained them – with the threat this could affect the institution's inspection grade.
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