Thousands of budding teachers never make it into the classroom, according to new research.
Many fail to finish training courses, while others struggle to find teaching jobs, it was suggested.
The Good Teacher Training Guide 2012 also reveals that high numbers of maths, science and languages teachers do not have good degrees in their subject.
11,000 teachers did not end up in posts in 2010/11
Researchers at Buckingham University's Centre for Education and Employment Research analysed official data on teacher training for the 2010/11 academic year, looking at where trainees study, the numbers entering the profession and the types of qualifications they hold.
The findings show that in 2010/11, 70.4% of 37,734 teacher trainees were in teaching posts the following January.
This means that around 11,000 did not enter the profession.
Of those that did become teachers, 60.6% went to work in state schools, 4.9% found jobs in private schools and 4.9% were in teaching, although the sector was unknown.
Report author Professor Alan Smithers said that for the year examined, teacher training was a two-stage process with individuals doing their training and then looking for a job.
"Some people start with teacher training and it becomes clear to them that they are not going to make good teachers, and others successfully complete and they're not necessarily able to find a job," he said.
Ministers have announced plans to overhaul teacher training, moving it away from universities into schools.
Tests in maths and English, which trainees must pass before they enter the classroom, are being toughened up, and in future will be taken before training begins.
The latest research also shows that teacher trainees in arts subjects such as history and English were more likely to have good degrees than those training to teach maths or science.
It found that 83.3% of history trainees had a first class, or upper second (2.1) degree, along with 78.5% of those training in dance and drama, and 76.9% if those planning to teach English.
At the other end of the scale, 49.5% of those training in information and communication technology (ICT) had a "good" degree, along with 52.5% of budding maths teachers and 54% of those training to teach science.
"It means that children are more likely to find themselves with knowledgeable teachers in subjects like history and English than in maths, the physical sciences and ICT," the report says.
It adds that trainees recruited to teach science were among the least well-qualified, with 20.2% of physics teachers holding less than a lower second (2.2) degree.
In chemistry this figure was 18.2%, and in maths in was 15.4%.
The report also found that subjects such as physics, chemistry, ICT and maths were more likely to have higher drop-out rates among trainees.
"In the case of the physical sciences and maths, one of the main attractions to studying those subjects is the love of abstract patterns, and of course that's a very different satisfaction from spending all of your days with 20 or 30 boisterous young people," Prof Smithers said.
"The people who are drawn to those subjects are not necessarily drawn to teaching."
The government has announced that new bursaries of up to £20,000 are available next year for people with top degrees to become teachers in subjects like science and modern foreign languages.
But Prof Smithers said: "For mathematicians and physicists, there are a lot of employment opportunities, even those very generous bursaries of £20,000 may not overcome this.
"It's a big short-term incentive, but it may not overcome the aspects that mathematicians and physicists may not necessarily enjoy teaching."