David Blunkett has launched a fightback against critics of the government's education policy.

Speaking on Tuesday, the education secretary said his opponents had "failed to understand" the importance of the government's early policies.

In a speech to the Institute for Public Policy Research, Blunkett said that the four years of progress achieved by Labour had paved the way for higher expectations and the modernisation of secondary education.

He called for vocational study from age 14 to be radically expanded from the current number of 50,000 studying vocational courses.

If Labour wins the next election, Blunkett said the challenge for the next term would be to raise standards and maintain accountability. He wanted good schools to play to their strengths and to free headteachers to lead and teachers to teach.

Blunkett also backed school inspections every six years to "maintain the balance between freedom and accountability".

He called for an end to old arguments, saying that they should now be laid to rest.

"There are those - on the right and left - who have not moved on from debates long since concluded and judge every development by their past preconceptions. But these commentators very often miss the point. These hoary old debates are lesser challenges than the real ones which have faced our system for decades and which this administration has started to address in fundamental ways," Blunkett said.

He blasted teacher training colleges for practicing "let it all hang out" training methods from the 1970s onwards.

"A peculiar notion grew that children could learn to read without being taught to read. This pedagogic distortion betrayed a generation of children," he said.

He hit back at claims by the Conservatives that staff were being bombarded by red tape. "Let's separate fact from fiction here. I read various descriptions of 10 circulars sent to schools in six months. Such claims are sheer nonsense," Blunkett told his audience.

The minister called for more administrative staff to carry out clerical jobs such as photocopying of teaching materials and praised staff who have improved low-achieving schools. "The number of schools now failing Ofsted inspections has fallen in this school year to 93 from 162 in the equivalent two terms last year," he said. "That is a huge achievement."

Blunkett concluded by saying that Labour's aim was to "deliver as profound an improvement in secondary schools" as that which has been achieved in primary schools.

Doug McAvoy, the NUT general secretary, gave a luke-warm response to Blunkett's remarks. "The government must not try to obscure the need to improve pupil teacher ratios by increasing the number of adults to pupils in our schools," he said.

McAvoy said: "This must not obscure the increase in workload for teachers caused by classroom assistants. The teacher has to manage, guide and advise classroom assistants if the benefits they can bring in helping the teacher deliver the curriculum and improve standards are to be realised."

The speech is likely to be Blunkett's last major public speaking engagement as education secretary, with many tipping him as Blair's choice for home secretary in a post-election reshuffle.

The Department for Education and Employment is also set for a revamp, with its employment functions likely to be transferred to a beefed-up Department of Trade and Industry early in the next parliament.