Careers education in two-thirds of schools is being led by staff who have no formal qualification in the subject, according to a critical report by MPs.
The public accounts committee called for improvements to Connexions, which has replaced local careers services and provides teenagers with pastoral and employment advice.
The committee said it felt that the pound;450 million-a-year service was doing good work helping 16 to 18-year-olds not in education or employment.
The proportion of young people in this category fell by more than 3 per cent last year.
But the MPs said there were "risks that the wider population of young people may not always get the advice they need".
Their report was particularly critical of the quality of career advice available in schools, which they said was too variable. They cited figures from a National Audit Office (NAO) survey which show that two-thirds of school staff who led careers advice had no qualification in the subject.
Half of the schools surveyed claimed they did not have enough time to fit careers advice into the curriculum. In addition, two thirds felt that their staff did not understand the role of Connexions personal advisers.
The MPs recommended that Connexions staff should work more closely with schools and provide regular training to help teachers identify pupils to refer to the service. They said the training should be supplemented with seminars in which teachers are shown real-life cases where teenagers have been helped.
The committee also recommended that Connexions partnerships should ensure that all their staff had completed training on how the service functions by next March. The NAO study found that half of the Connexions advisers they surveyed had not completed the expected training.
The DfES has been conducting a review of careers education which will be included in its Youth Green Paper, due to be published in January. A spokeswoman said the department was addressing the committee's report and was glad it had highlighted Connexions's success with young people out of education.