the quality of on-the-job training for new teachers is sub-standard in most secondary schools, with trainees often failing to teach their subjects effectively, a report by inspectors has found.
The review by Ofsted, the school standards watchdog, said there were unacceptable variations in the quality of training and that mentors are often too busy to properly support new teachers.
One in six teachers join the profession via the graduate teacher programme, through which new teachers are attached to schools.
The three-year review found that secondary trainees were less skilled at teaching subjects than peers who completed the more traditional post-graduate certificate in education.
In subjects with staff shortages, such as maths and science, this had led to teachers making basic errors in class, the report said.
"Subject training is not good enough in the great majority of providers,"
the report said. "Mentors' expectations of trainees are frequently too low and they do not do enough to develop trainees' ability to plan for and assess subject-specific learning."
Although teaching standards had improved compared with the previous year, one in six lessons in 2005-06 still suffered from significant weaknesses.
The programme, which pays graduates a salary, was introduced in 1997 to attract more mature entrants to teaching. But it has suffered consistent criticism recently for failing to prepare teachers for the job.
"The auditing of secondary trainees' subject knowledge continues to be a major weakness," the report said. Trainee teachers often misjudged their own knowledge, especially those with gaps in their subject knowledge.
The portfolios that trainees had to produce to show they were reaching the right standards were often "not fit for purpose", and training was not designed to meet individual needs, the report added.
But inspectors, who visited more than 680 schools and observed more than 480 lessons over the past three years, said that there had been some improvements and praised the range of experience trainees gained from being involved in school life.
They knew more about professional responsibility and were better at managing pupil behaviour than their PGCE peers, the report said. The provision for primary school teachers was also better than in secondary schools.
John Bangs, head of education at the National Union of Teachers, said insufficient funding meant that trainees and their mentors could only spend a limited amount of time together.
"Mentors have to grab time in the already crowded timetable and tutoring is often limited," he said. "Higher education courses give more substantive tutorial time."
"The quality of the training is variable from school to school, but that's nothing to do with the quality of the recruits," he added.
A spokeswoman for the Department for Education and Skills said it would work with the Training Development Agency to improve the programme.