Popular vocational business studies courses taken by thousands of pupils contain serious flaws and leave students with "weak" levels of knowledge and understanding, according to a damning Ofsted report.
Inspectors raised concerns that the courses, claimed to be worth between two and four GCSEs, are not rigorous enough and use "narrow and simplistic" assessment criteria.
The findings came in an evaluation of economics, business and enterprise education in schools and colleges between 2007 and 2010. They come just weeks after education secretary Michael Gove announced plans to reform vocational education.
Inspectors have recommended that the Department for Education and exams regulator Ofqual review the equivalency of vocational business courses, which include Btec courses and diplomas.
"Evidence from lesson observations, scrutiny of written work and discussion with students brings into question the case for claiming that such courses are equivalent to between two and four single-award, traditionally examined GCSEs at key stage 4," the report said.
Ofsted also identified concerns that pupils on vocational courses do not get as much teaching time as those studying traditional GCSE and A-level qualifications. Even students achieving good results often had weak levels of understanding, inspectors found.
More than 17,800 pupils took the BTEC first certificate in business last year, according to Ofsted. Over a third of candidates gained a distinction, equivalent to two GCSEs at grade A* and A. All students got a pass grade or above, the equivalent of two GCSEs at grade A* to C.
Following the recent Wolf report, the Government is reviewing which vocational qualifications should be included on school exam league tables. External assessment is set to be introduced for the first time to Btecs, which are currently teacher assessed with external moderation.
Ofsted chief inspector Christine Gilbert said: "Vocational qualifications provide a valuable route to employment and further study for many learners. However, the report highlights the need to review the equivalency of vocational business qualifications that are assessed wholly or mainly by internally set and marked assignments."
A spokeswoman for Pearson, which owns exam board Edexcel, said she was pleased that the report found well-taught vocational courses could help students develop employment skills.
A DfE spokesman said: "This report raises serious concerns about the quality of some courses taught in our schools.
"This summer, we will be carrying out a consultation on the characteristics of high-quality vocational qualifications so we can ensure that only those qualifications that meet the criteria are taught."