Results of the Sats in reading and maths, taken by more than 500,000 pupils this week, will be used to judge whether schools are failing or not.

If primaries do not reach a certain “floor standard”, they may be forced to convert into academies. If they are already an academy, their sponsor may be changed.

In 2016, when tougher Sats were first introduced, the number of schools below the floor standard was 665 - around 5 per cent of state-funded primaries.

But, because of the changes made to primary assessment, the government added that decisions on academisation and other interventions were not to be made on the basis of the test data alone.

The figure was a fall from previous years. In 2006, more than 2,000 primaries were below that year’s floor standard. Part of the reason for the drop since then has been a broadening of the target that schools have to meet - enabling them to show pupil progress rather than just attainment.

The figure fell in 2010, when a quarter of schools boycotted the tests. And a plunge in the number of schools missing the standard in 2012 coincided with a move from external testing to teacher assessments for writing.

But the following year, numbers missing the floor standard rose as the standard was changed again. Schools were expected to take 60 per cent of pupils to level 4 or above in both reading and writing, rather than achieve an average of 60 per cent across both for a combined English score.

In Scotland, there is no floor standard. But teachers assess how pupils are progressing in reading, writing, numeracy and listening and talking. The number of pupils reaching expected standards in each of these at the end of primary was reported for the first time last year.

@teshelen