Ed Balls picked up some painting tips from students at the college
Ministers have renewed their effort to promote the new Diplomas as figures showed the number of pupils taking the first is half what they had hoped.
England's Schools Secretary, Ed Balls, went to a community college in north London, stressing the importance of the quality of learning over quantity.
Officially there is no target for the first five Diplomas beginning this autumn but 40,000 had been expected.
Figures being released during the visit showed the total signed up is 20,000.
The ''ballpark figure'' Schools Minister Jim Knight gave to the Commons education select committee last year for the take-up by teenagers in the first phase was 50,000.
He did stress at the time: ''It is not a target.''
The director of the 14-19 reform group at the Department for Children, Schools and Families, Jon Coles, told the MPs that if all the consortia that had expressed an interest in offering diplomas were successful, the figure could be ''in the region of 160,000''.
More recently the department has been talking about 38,000.
Staff at the college say construction job opportunities abound
But Mr Balls was bullish as he toured the college, visiting students on painting and decorating and automotive courses.
"We decided the right thing to do was to make sure we put quality first, that we move forward with schools and colleges who really were confident in the first year that they were ready.
"Any school or college who said they needed more time, we said: 'That's fine by us'."
Andy Powell, chief executive of practical learning charity Edge, said: "That fewer students than expected have signed up to diplomas should not be seen as the failure of the qualification," he said.
"They present the chance to re-engage young people with their education by providing vocational and practical learning alongside the academic path.
"We should recognise that diplomas are a complicated thing to deliver and get behind those students who have signed up to them."
The general secretary of the Association of School and College Leaders, John Dunford, said the numbers of pupils would be "of secondary importance" if the courses were high quality.
"Schools and colleges have put an enormous amount of work into getting diplomas off to a good start," he said.
"It is considerably more complex than putting on a new A-level, not least because of the partnership arrangements between schools and colleges which inevitably create logistical problems."
At the same time, the university admissions service, Ucas, has said one in three higher education institutions has provided statements backing the Diplomas.