The new, more flexible, primary curriculum risks widening the achievement gap between the lowest and highest performing schools, the official leading the reform has warned.
The Qualifications and Curriculum Development Agency has also told local authority officials that implementation will have to be carefully monitored because some heads are wrongly interpreting the new curriculum as a return to 1970s and 1980s-style topic-based teaching.
John Crookes, a senior curriculum manager at the agency, said there was a danger that lower-performing schools would fall further behind high- achieving counterparts that had the ability to make the most of their new freedoms.
"How do we counter that?" he asked local authority officers and education consultants. "Left to itself, that gap will widen. How do we secure those schools who lack agency, lack confidence?"
His warning came as a senior civil servant at the Department for Children, Schools and Families admitted there was already a divide between how schools interpreted their existing curriculum freedoms.
Jon Coles, director general of schools, told a meeting organised by the Commons schools committee: "Good and outstanding schools in the system are tending to take much more advantage of the flexibility that is out there than other schools."
Critics of Sir Jim Rose's proposed new primary curriculum have already argued that it amounts to a return to the kind of topic work that the so- called Three Wise Men report he jointly authored in 1992 described as "fragmentary and superficial".
Now the QCDA has revealed that some schools share that analysis of the reforms. Mr Crookes, who worked on the Rose review and now leads the team responsible for its implementation, said: "Some heads do think this is `back to what we know - topics'. But it is not."
The new curriculum is less prescriptive on the content schools must teach. By the time it is introduced in September 2011, the National Strategies - a major government instrument for influencing teaching - will have been disbanded.
"The issue is how we secure entitlement for children in a time where delivery models and central prescription models are being removed," Mr Crookes said, speaking to local education officials at an Association of Professionals in Education and Children's Trusts (Aspect) conference seminar.
"That is quite popular. But there are risks associated with it, so how do we minimise those?"
Sue Foster, a council member of Aspect, said some high-performing primaries would take the new flexibilities offered and run with them.
But others would be looking for guidance from local authority advisers on what to do. There was a danger that those advisers, used to delivering National Strategies material to schools, could simply fill the gap with their own content.
"You could go from a nationally prescribed curriculum to one that is locally prescribed," she told the seminar.
Speaking afterwards, Mr Crookes said that to avoid the achievement gap widening would require "accurate and diagnostic" monitoring from Ofsted and local authorities.
"It is the same issue running across all areas of education policy at the moment," he said. "What happens when you take the policy controls off? You can't go back to how things were.
"That is why it is still important to say we do need phonics. It (should not) just be (schools) deciding what they want to do."