The college's principal, Bill Moorcroft, said: "The grammar schools are comfortable doing what they do. I don't believe in the first instance they will show any interest in specialised diplomas."
He believes only a quarter of pupils will opt to take one. "On that basis, the colleges are critical, because without them the 14 subjects won't be offered as they won't be cost-effective."
Ofsted has declared South Trafford College outstanding, with grade 1s in all five inspection areas. It is also a Centre of Vocational Excellence in healthcare. Despite its specialist facilities and expertise, headteachers of some of the borough's non-selective schools want to offer diplomas in their own classrooms.
Another issue that concerns Mr Moorcroft is competition. A school three miles from the college has just won approval for a new 300-place sixth form. "The intention of the school is to offer a similar curriculum to colleges. So it becomes quite difficult to collaborate with somebody that is possibly your competitor."
In contrast, Wolverhampton has taken a strategic approach. The area was among the first to test 14-19 education partnerships, so collaboration between the City of Wolverhampton College, the only FE institution locally, and 18 secondary schools, all with sixth forms, is well-established.
Key to its success has been the role of a 14-19 co-ordinator in the local authority in helping to agree practicalities, such as common timetabling and transport between institutions. The city also runs events allowing year 10 and 11 pupils to go into colleges, training providers and other schools to sample what is on offer.
City of Wolverhampton College takes a lead role locally in the new diplomas, chairing four of the five development groups.
The principal, Ian Millard, said: "For me, the development of those groups was an acid test of the partnership. If it had been all schools taking the lead on them, it might well have been perceived that we were guests at the party, rather than the hosts."