Commenting on the news that SATs results, which were due to be with schools by Tuesday next week, have been delayed, Paul Whiteman, general secretary at school leaders' union NAHT, said:

“This delay is completely unacceptable. Schools will have made careful plans for results day and it is totally unfair to land this on them at the last-minute, especially when teachers are expected to produce end of term reports for pupils and parents are waiting for results.

“The kind of issues arising from a change in contract supplier should be entirely foreseeable, and although we repeatedly highlighted the risks to the Standards and Testing Agency (STA) we were reassured that everything was on track.

“Clearly, though, something has gone badly wrong and Pearson has questions to answer. We would expect serious consequences to follow.

“Given reports of issues with marking, and with the end of term approaching, it’s vital not only that the the situation is resolved as quickly as possible but also that accurate results are returned. Schools must be given cast iron assurances that the results they receive are reliable.

“Schools are held to an extremely high standard when it comes to test administration. Small errors can result in serious consequences for school leaders, and the same should be expected of Pearson and everyone responsible for test and exam results.

“This is not the first time schools have faced delays, but once the current issues have been addressed it is vital that they are properly investigated to ensure it is the last. Pupils, parents and schools have been badly let down. Given the fiasco around the marking and return of results, we once again question the whole purpose of these outdated tests.”