Schools have worked "miracles" to achieve good results amid a tumultuous year for primary education, according to headteachers.

Teachers and pupils deserve "great credit", they argued, as new figures showed that almost 200,000 youngsters are being taught at schools which are considered to be under-performing.

Pupils across England took new, tougher SATs tests in reading, writing and maths this year, following the introduction of a new primary curriculum.

But the move has been fraught with controversy with teachers and school leaders raising a number of concerns, including a lack of information for teachers, the difficulty of the papers, leaks and the unreliability of results.

Statistics published today show how every primary school in England has performed against a new Government floor target.

School standards minister Nick Gibb said the new curriculum has raised standards, and many schools had responded well to it.

But one union leader today warned that the data "is not worth the paper it is written on".

In total, 665 mainstream primaries in England fell below the Government's floor standard this year, according to the Department for Education (DfE).

Schools are now considered under-performing if fewer than 65% of pupils fail to reach the expected standard in reading, writing and maths, or if they fail to make sufficient progress in these three key areas.

Overall, 5% of primaries fell below the Government threshold this year.

Education Secretary Justine Greening had previously pledged than no more than 6% would be below the benchmark. She also promised that no school would face outside intervention based on this year's data alone.

According to Press Association analysis of the data, around 180,743 children are being taught at the 665 primaries that failed to meet the Government's new threshold. This is around 4.1% of the total number of youngsters at mainstream primary schools in England.

Across England, 53% of the almost 600,000 11-year-olds who took the tests reached the expected standard in reading, writing and maths this year.

Mr Gibb said: "This year's SATs are the first that test the new primary school curriculum in English and maths that we introduced in 2014.

"This new curriculum raises expectations and ensures pupils become more accomplished readers and are fluent in the basics of arithmetic, including times tables, long division and fractions.

"Many schools have responded well to this more rigorous curriculum, supporting their pupils to be leaving primary school better-prepared for the demands of secondary school."

But Russell Hobby, general secretary of the National Association of Head Teachers (NAHT), said: "This data is not worth the paper it is written on.

"The Government itself has said that it cannot be used to trigger interventions in schools, nor can it be compared to previous years."

He added: "This year, we saw the SATs system descend into chaos and confusion. Delayed and obscure guidance, papers leaked online, mistakes in test papers and inconsistent moderation made this year unmanageable for school leaders, teachers, parents and pupils.

"The data gathered in primary assessment during 2016 is misleading. We warned the Government that publishing this data in league tables could lead the public and parents to make poor judgments about a school's performance, but it has still chosen to do so."

Julie McCulloch, primary specialist at the Association of School and College Leaders, said: "The goalposts have shifted this year and these results have to be viewed in that context.

"The tests are based on a new, much harder curriculum, which the children had followed for only two years, and the expected standard has been significantly raised. In addition, the Government's introduction of these tests has been chaotic.

"Against this background, schools, teachers and pupils have performed miracles and deserve great credit."

Previously, pupils were awarded "levels", with Level 4 the standard expected at the end of primary school. These "levels" have been scrapped and students are expected to reach a new standard based on scaled scores in each subject. The new expected standard has been set at a higher benchmark than the old Level 4.

In May, the answers to the Key Stage Two grammar, punctuation and spelling test appeared on a password-protected area of an exam board website for several hours before being removed.

A ''rogue marker'' was blamed by the Government for the attempted leak.