Pupils' knowledge of the business world is being compromised because teachers have too little understanding of the subject, inspectors have said.
A study of the first two years of the applied business GCSE found that pupils' work was too often lifted from firms' websites.
David Butler, subject adviser for the Office for Standards in Education, said lessons did not challenge pupils enough and too many teachers, particularly in 11-16 schools, did not have the qualifications to teach business. As a result, pupils' coursework fell short in the areas of analysis and evaluation of companies' actions.
"If you do not have business knowledge, it is very difficult to teach it," he said.
Pupils' achievement was satisfactory in all lessons seen by inspectors, but few were good. In traditional GCSE business courses, more than half of lessons were good. High-attaining pupils in particular underachieved.
Ofsted's findings were based on visits to 18 schools in the past two years as part of a wider investigation into the eight new vocational GCSEs, published this week. The courses, which will replace General National Vocational Qualifications, were introduced in 2002 and final exams were taken for the first time this summer.
Mr Butler said poor links between schools and businesses meant that teaching of the vocational part of the course was "rarely good".
Ofsted found that applied business had proven popular with a broad cross-section of pupils who were generally well motivated. The course was winning parity of esteem with other GCSEs.
David Hart, general secretary of the National Association of Head Teachers, said: "The Government has not put enough emphasis on training teachers for vocational education."
Chancellor Gordon Brown wants all pupils to learn about business. The Government is spending pound;25,000 on 35 pathfinder projects to pilot enterprise education. But schools say that budget constraints limit opportunities.
At Great Sankey high school, Warrington, which is involved in one pathfinder scheme, about 60 pupils had to compete for only 30 places.