A quarter of 607 English schools the government is threatening to close were graded "good" by inspectors, and 16 were judged to be "outstanding".

Only one in 10 was regarded by Ofsted as needing intervention, analysis by the National Union of Teachers shows.

Ministers are targeting schools where less than 30% of pupils get five good GCSEs, including English and maths.

NUT leader Christine Blower said the analysis showed just how "shocking and random" this arbitrary level was.

Last week the government published a list of 638 schools that fell below this "floor target".

The union was able to check published Ofsted reports on 607 of the schools - which are to get extra funding in a "national challenge" scheme to raise their results.

Of the 31 for which no report was available, 14 - almost half - are academies.

These state-funded independent schools with sponsors drawn from churches, businesses, universities or other organisations, are the government's preferred alternative to what it sees as underperforming schools - but only in England.

But the NUT points out that there are 27 academies on the Department for Children, Schools and Families list of 638 schools.

'Headline-grabbing measure'

The union says it cannot be right that £260m of the £400m earmarked for this drive is to be spent on establishing more academies or trusts.
"It seems to me that the government has decided to junk its recent attempts to introduce a measure of sophistication into evaluating schools in favour of a crude headline-grabbing measure to try to show that it is tough on standards," said Ms Blower, the NUT's acting general secretary.

"The support outlined in the National Challenge programme will be obscured by this injustice.

"Teachers and head teachers will be very wary of wanting to join schools that could be threatened with closure.

"The NUT will not stand by and watch the vilification of school communities and the intolerable pressure put on heads and teachers as a result of the government's arbitrary actions."

School closures would be resisted and the union's members would be protected from excessive workload demands, she added.

As well as giving extra support to the schools on the list, the Department for Children, Schools and Families does say that many of the schools are on their way to having results above the 30% level.