The move follows bitter disputes between institutions allegedly withholding information from others in the recruitment wars.
Last February, for the first time in more than 10 years, Runshaw College staff were not allowed into Hutton grammar, near Preston, to tell year 11 pupils about courses on offer just five miles away.
The school, which owes Lancashire Country Council more than Pounds 300, 000 after running at a loss for two years, partly blames its cash crisis on a loss-making sixth form. "Relations are not very good," said college principal Bernard O'Connell. "We don't have that much to do with one another."
Education ministers may call for co-operation on careers but colleges say the survival message is one of increasing competition.
Sixth-form colleges in East and West Sussex have joined forces to produce a video promoting the benefits of switching from school to a sixth-form college when students reach 16. The video, which will be shown at open evenings and presentations to pupils, will be particularly important in attracting students from schools with sixth forms which do not allow colleges to come in and publicise their courses.
"It will help us with those students who are difficult to reach," said Harvey Linehan, marketing manager at Brighton, Hove and Sussex Sixth Form College. Prospective students sometimes enquire about a course too late to attend an open evening.
Six colleges within a 30-mile radius of one another paid around Pounds 2,000 each towards the cost of producing a 10-minute video featuring its own students. The first 2-3 minutes, extolling the general value of a sixth-form college education, will be common to all six versions.
Mr Linehan, who co-ordinated the project, said colleges wanted to stress the breadth and diversity of the curriculum, the quality of teaching and the individual support offered to students.
Although Haywards Heath College does not compete against 11-18 schools, it competes with other colleges, including some of those which helped produce the video. It also wants to stress the importance of 16-year-olds remaining in full-time education.
David Hewer, marketing and enterprise manager, said the six colleges had each gained a professionally-made video at a fraction of the cost. "It's a corporate attempt to focus young people's minds on continuing their education, but each college had its own story to tell."
About one third of Brighton and Hove Sixth Form College students come from 11-18 schools in Hove. Varndean College, Brighton, which was also involved in the project, has a code of conduct with the sixth-form college which states that neither institution should make comparisons with one another but point to their own strengths.
Brighton and Hove principal Vaughan Williams, who said the video should also help attract students from independent schools with sixth forms, said post-16 competition was fairly fierce, even before incorporation. "Principals elsewhere say they are horrified about more schools opening sixth forms, but we have already been there and done that."