A report into the Information, Advice and Guidance (IAG) service says advice given in colleges is worse than that given by external providers such as Connexions.
The Local Government Association (LGA) commissioned the National Foundation for Educational Research to look into the current state of IAG services provided for 14- to 19-year-olds.
"Lower levels of confidence were reported in terms of school and college IAG provision in contrast to external provision," it said.
The president of the Institute of Career Guidance, Deirdre Hughes, said the findings reiterated the need for schools and colleges to better formalise their working arrangements with external careers advisers.
"We believe a formal working arrangement between a school and external provider, such as Connexions, makes a significant contribution towards supporting individuals' social mobility and economic prosperity," she added.
Mrs Hughes said the survey had shown that careers advice offered to teenagers within schools and colleges was "patchy" and added: "It's very, very variable depending on which school or college children go to."
Mrs Hughes said she would be telling the Government that partnerships between colleges and Connexions needed to be improved when she meets them next week as part of her role on the Careers Profession Taskforce.
The report also found that IAG services were widely reckoned to contribute to raising learners' aspirations and said that partnership working was key to the effective delivery of IAG. Good IAG was characterised by fully trained and qualified staff, it added, and senior leaders in schools, careers co-ordinators, form tutors and other staff should be trained in current policy.
But it said a lack of resources was hampering efforts to provide a universal service for teenagers as well as concentrating efforts on vulnerable groups.
Last week's report came out alongside a companion survey for the LGA by the National Youth Agency, covering the London and South West regions, which revealed that youngsters thought youth workers were the best people to give advice.
But Mrs Hughes warned that youth workers should not double up as careers specialists in the wake of budget cuts at Connexions. The Government agency has already begun to see local authorities take the axe to its budgets as part of the coalition Government's austerity drive.
"I'm sure our colleagues in the youth service don't welcome the idea that they might have to become a careers expert," Mrs Hughes said. "It is like saying careers advisers should do the work of youth workers. They are not trained to do that."
But a spokesman for the National Youth Agency, Jon Boagey, said: "Young people identify youth workers as a valuable source of advice because of their independence and perceived impartiality."