A new testing system to replace SATs in state schools has been hit by ‘substantial and fundamental’ problems, according to a report.

Pilot tests taken by 100,000 children in the last 18 months have faced severe problems, giving wildly unpredictable results and exposing children to even more high-pressure testing, the two reports conclude.

The government is piloting the ‘single level tests’ (SLTs) in response to criticisms that the current system of SATs is too stressful for schools and pupils and does not provide high-quality information about their capabilities.

The scheme was designed to allow pupils to take tests at their own pace between the ages of seven and 14, instead of en masse at the ages of 11 and 14.

However, two unpublished reports on the pilot system, which were carried out by the National Assessment Agency and five independent academies, have revealed serious problems.

According to the Guardian, which has seen the reports, there were particular flaws in the maths and writing tests with some primary school children outperforming those at secondary school five years older.

The academics suggested the reason for the problems stemmed from the fact that the tests relate to the curriculum learned in primary school. By the time the pupils reach secondary school they have forgotten much of what they have learned in primary so cannot answer many of the questions.

Because the tests are designed to be taken flexibly when children are ready, rather than at a certain age, they raise great problems about how to match the tests to the curriculum.