Work-related lessons for teenagers have improved dramatically in just a year as schools have got to grips with them, Ofsted will announce today.
But the education watchdog will warn that too many secondary teachers are still not properly trained for vocational lessons, which are now compulsory in all secondary schools.
Ofsted's major inspection of key stage 4 teaching will show that the curriculum for 14 to 16-year-olds is good in more than half of schools.
Only last year, inspectors criticised standards of teaching in new work-related courses, describing them as unsatisfactory in 20 per cent of lessons. That figure has now fallen to just 6 per cent.
Schools providing a wider curriculum reported noticeable effects on their pupils, including better behaviour and attendance, particularly among children becoming at risk of disengagement.
But Ofsted said that a significant minority of schools - about 15 per cent - were failing to offer a broad curriculum, often because they were too focused on league tables and exam performance. Schools that provided an inadequate curriculum offered few or no vocational courses or leaving out important areas such as ICT.
Schools have been under increasing pressure to provide work-related courses ahead of the introduction of specialised vocational diplomas next year.
Since September 2004 all schools have had to provide 14 to 16-year-olds with vocational courses, such as business studies and ICT, as well as careers advice and work experience.
Inspectors visited 155 comprehensive schools and eight colleges for the two-year review, including grammar and special schools, which they said represented the national picture.
"Too many (teachers) were insufficiently acquainted with the demands of the qualifications they taught. This affected their ability to assess work accurately and help students improve," the report said.
Steve Sinnott, general secretary of the National Union of Teachers, called for better training for teachers taking vocational courses.
"We have consistently said that there is a lack of appropriate training for teachers who take on these extra responsibilities and more administration time is needed to organise pupils' work experience placements," he said.
And a third of schools were pushing pupils too heavily towards vocational or traditional academic routes based on their exam results in Year 9, the report said.
Judith Smith, headteacher of Babington community technology college in Leicester, said: "The original key stage 4 academic curriculum was supposed to be one size fits all, but it didn't. Introducing work-related learning has been exciting."
Inspectors said schools, colleges and other education providers would need to work together more closely to make a success of the new specialised diplomas.
Leading the field: page 7