Ministers have been warned not to neglect underperforming primary schools.

Education watchdog Ofsted released a report on Tuesday which found that literacy and numeracy teaching for under-11s has continued to improve in the majority of classrooms.

But the schools inspectorate cautioned against complacency after finding a "stubborn core" of one in eight lessons remain unsatisfactory.

In addition one third of schools are still only at a "satisfactory" level despite the investment in reading, writing and arithmetic since Labour came to power in 1997.

The government's dedicated literacy and numeracy hours scheme has been widely hailed as a success but Ofsted warned there are still too many schools where performance could be improved.

The report highlighted an excess of "teachers' talk" and a lack of specialist English and maths knowledge among primary school staff as particular impediments to progress.

Ministers should "continue to provide support for local education authorities in dealing with schools where leadership and management are weak" the authors argued.

They should also "direct attention and resources to underperformance in LEAs and schools, and support LEAs and schools in improving the quality of teaching and assessment for learning".

Efforts to meet ministers' commitment to reaching ambitious minimum targets with extra resources being focused on poorly performing pupils were also assessed critically.

"There has been a strong emphasis on intervention programmes and 'booster' provision to raise attainment," the report found.

"However, in too many instances, these are not targeted effectively and schools have not evaluated their impact on pupils' attainment sufficiently."

But the report concluded that the introduction of the national literacy and numeracy strategies in England has been a success.

"The positive aspects are outweighing the negative," Ofsted said.

Schools minister Stephen Twigg welcomed the report.

"Through the hard work of teachers and pupils and the impact of the national literacy and numeracy strategies, there has been a step change in primary results over the last six years," he said.

"Everyone would like to see faster progress for those 11-year-olds not currently reaching the expected standard, but I am confident that the measures in place to raise primary school standards further are the right approach.

"Most of the challenges Ofsted identify we are already tackling through Excellence and Enjoyment, our strategy for primary schools published earlier this year.

"As part of this, schools will be urged to take a fresh look at their curriculum, their timetable and the organisation of the school day and week, and think about how they would like to develop and enrich the experience they offer their children across the curriculum."

But teachers' union leader Eamonn O'Kane said Ofsted should do more to talk up the work of classroom staff.

"The comments of the chief inspector will do little to boost teacher morale or improve retention within the profession," the NASUWT general secretary said.

"Seven out of eight classes have been shown to be satisfactory or better and the vast majority of results have remained at the same level or improved.

"Where there are problems it is quite clear that extra resources should be deployed to help schools and teachers.

"Teachers work to a set of performance targets determined by government. Ofsted should hold the government to account for its literacy and numeracy strategy rather than undermining the work of teachers who have held results steady for another year."

A separate report on pupils from traveller families found that as many as 12,000 children are not going to school.

Ofsted found the average attendance rate among the group was 75 per cent, below the overall national rate and the worst of any ethnic minority group.

Chief inspector David Bell said a combined effort throughout the education system was needed to get to grips with the problem, which was particularly evident in secondary schools.

"I am very worried by the findings of this report," he said. "Traveller children are being denied the education they need in order to make informed choices about their future careers.

"Not enough traveller pupils stay for any significant period in secondary school.

"Traveller pupils linger on the periphery of the education system. The alarm bells rung in earlier reports have yet to be heeded.

"There needs to be a concerted effort by the government, local education authorities and schools to address this issue."

The report recommended ministers give more assistance to LEAs on the education of travellers' children at home, which is a popular choice among parents.