More Diplomas will be available this September
Some of the teaching of the new 14-19 Diploma in England needs to be improved, government inspectors say.
Ofsted found the quality of teaching of functional skills - maths, English and information and communication technologies (ICT) - needed attention.
They also noted Diploma choices tended to be along "traditional gender lines" and said advice for young people on the courses could be improved.
The government said colleges and schools were receiving more support.
The inspectors said work was "no better than satisfactory" in construction and the built environment, but generally good on the other courses.
Diplomas are delivered by a collaboration between schools, colleges, employers and other training providers and are available in four levels.
Inspectors visited 23 groups of providers teaching the new Diplomas between September 2008 and March 2009 - including schools, colleges, and employers.
They noted that in 19 of these areas, the number of young people not in any education, employment or training has been reduced since the 14-19 education reforms were introduced.
And they found that most students they came across were "well-motivated" by the applied nature of their learning.
Students benefited from good involvement of local employers in most of the courses observed, they said.
But the inspectors had concerns, including about the quality of outside collaborators.
Inspectors found that implementation of the core content of the Diplomas was good in half of the courses observed, outstanding in one and satisfactory in the remainder.
However, they voiced concerns regarding the additional and specialist elements of the courses.
They said: "In contrast to the principal learning component of the Diplomas, work in functional skills lacked coordination in just under half the consortia visited and, as a result, the quality of teaching and learning varied considerably."
These skills were "central", they added, though not all students realised this.
Diplomas were introduced in September 2008, as the main plank of the government's 14-19 education reforms, together with a focus on separate qualifications in functional skills.
Five Diploma subjects are available, in construction and the built environment, creative and media, engineering, information technology and society, health and development.
But take-up has been below what may be expected, inspectors said, particularly in the highest level.
The inspectors also noted that choice of Diploma was frequently along "traditional gender lines", with very low numbers of female students (3%) on the engineering course and the construction and the built environment course.
Their report recommends more focus on guidance for students on "avoiding unnecessary gender-stereotypical choices of Diploma".
The NASUWT union said teachers should not be blamed for the lack of clarity regarding the role of functional skills.
General Secretary Chris Keates said judgements about Diplomas were "premature" until all courses had been introduced in 2013.
"More work needs to be done to support teachers and all staff in schools to make use to an even greater extent of the wide range of learning experiences that the Diploma has the potential to offer," she said.
A spokeswoman for the Department for Children, Schools and Families said: "While we are pleased with the progress made so far, we acknowledge that more needs to be done to improve the teaching of Diplomas, which is why we are increasing our support for schools and colleges."