Teachers who train on the job lack the skills and subject knowledge to stretch pupils, Ofsted said this week.
Between a third and a half of lessons planned by teachers on the graduate teacher programme failed to challenge pupils, and one in five had unsatisfactory features.
Ofsted said teaching quality had not improved despite similar criticisms in a report last January.
The GTP promises prospective teachers "training tailored to your own individual needs" and a salary of at least pound;14,000 a year. It was introduced by Labour in 1997 to attract mature entrants to the profession.
About one in six of the 40,000 teachers trained each year come through the programme.
Trainees spend most of their time in schools, but many also attend a partner training college.
But the scheme has been dogged by concerns over quality. As The TES revealed last month, one in 10 of the so-called "designated recommending"
bodies that run training programmes has closed in the past two years after criticism from Ofsted. In the latest report, inspectors praised improvements in primary training and management and said trainees "were often more confident in managing pupils' behaviour than those trained through post-graduate certificate in education courses".
The GTP was also successful in attracting applicants to secondary shortage subjects, it said. But that was offset by weaknesses in training and recruitment methods.
About a third of secondary providers had weaknesses in subject-specific training, and many failed to check whether applicants had enough subject knowledge.
The report said: "In maths the auditing of trainees' knowledge was often superficial, amounting to little more than a simple checklist completed by the trainee, even where trainees held degrees that included very little maths."
Many providers failed to give trainees sufficient experience of different teaching styles, the report said, resulting in a narrower repertoire of teaching methods than among PGCE students.
Religious education trainees in faith schools often lacked the skills to teach the subject in other schools, and PE students lacked experience of swimming and outdoor adventure activities.
Ofsted said that 19 of the 47 providers inspected failed to meet individual training needs.
In particular, teaching assistants and others with classroom experience did not always have their needs accurately assessed.
Miriam Rosen, Ofsted director of education, said: "The GTP helps trainees develop classroom management skills quickly and those who choose this route are often more confident with discipline problems. But more attention needs to be paid to developing trainees' ability to teach their subject to a high standard."
A Department for Education and Skills spokesman said the scheme was rigorously monitored and no under-qualified teacher would get into the classroom.
"Since the report was written, 32 of the 47 designated recommending bodies examined have met standards, three have discontinued, and the rest are under scrutiny by the Training and Development Agency for Schools," he said.
Chris Keates, general secretary of the NASUWT, said: "The only purpose this report serves is to undermine the position of those who have undergone employment-based teacher training. It is unacceptable to imply that either these trainees or the training are second-class."
An employment-based route into teaching 20042005 is available from www.ofsted.gov.uk