Major problems with tests - claim

The pilot tests have been taken by some 100,000 pupils in 400 schools

There are fundamental problems with the testing system that might replace Sats in England's schools, it is claimed.

Draft reports on single level test (SLT) pilots say it is "very probably impossible" to achieve the aims of assessing attainment regardless of age.

One insider said it had been "unethical" even to have conducted the pilots, they were so flawed.

The government would not comment on leaks but said its testing experts had recommended continued trials.

"It is important to remember that single level tests are still being piloted and have not been rolled out nationally," a spokeswoman said.

"Piloting gives us the opportunity to constantly review and evaluate, so that we can iron out any problems and make sure that this type of testing is as good as it can possibly be."

'More testing'

The Guardian said the two leaked reports from the National Assessment Agency said that the pilots - undertaken in about 400 schools - had been rushed, results were erratic and ministers had not addressed warnings of "substantial and fundamental" problems.

An expert familiar with the SLT pilots has told BBC News that a combination of SLTS and internal progress assessments in schools would result in children being tested more often.

A big complaint from teachers is that they are obliged to "teach to the test" with existing Sats, narrowing the curriculum.

The expert said this would worsen if SLTs were to be implemented across the system.

Nor would the tests measure progress over time, as ministers intended, because they would be likely to produce erratic results - swinging from year to year and giving no coherent trend.