Schools have also been authorised to place less qualified teaching assistants in charge of classes to cut teachers’ working hours.

Teachers meeting at the annual conference of the Professional Association of Teachers in Buxton, Derbyshire, had said earlier that moves to cut their workload by giving a bigger role to classroom assistants could damage teaching standards, particularly in primary schools.

Under the National Workforce Reform Agreement, which has been phased in over three years, teachers will be entitled to set 10 per cent of their working week aside for planning, preparation and assessment, known as PPA time.

However, several head teachers claim that they cannot implement the reforms because of a lack of funding and have called on the Government for more money to hire extra staff.

Speaking at the conference yesterday, Jacqui Smith, the Schools Minister, insisted that the workload agreement would improve teaching quality. She said that extra money for primary schools had been successful. “The effect of that seems to be schools are able to implement it in a way we’d hoped and I hope to see that reflected in continued and improving results,” she said.

However, when asked if she accepted that some children could face being in classes of 60, she refused to rule it out, saying: “It’s important that head teachers make the right decision for their schools.”

The legal limit for 5 to 7-year-olds is 30 to a class.

Ms Smith said that 99 per cent of the 22,000 schools in England had shown that they were able to meet the requirements in September. Only 35 schools had said they had no plan yet to implement the programme and a further 180 had sent no data to the Department for Education and Skills.

Earlier, delegates of the 35,000-member union had voted overwhelmingly in favour of a motion stating that cutting working hours “may lead to a negative impact on the quality of provision” in the primary sector.

Kathleen Barraclough, head teacher of St Anne’s Catholic primary school in Surrey, said that in her area less than a quarter of local schools were providing PPA time. She feared that to do so, some teaching assistants “may be put into situations for which they are neither experienced nor trained”.

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