Principals Federation president Philip Harding, says some schools are using dodgy strategies to boost their results in the national standards in reading, writing and maths.
The federation says it has been told of children re-sitting tests if their scores are too low, and of teachers prompting children to improve their scores on reading tests.
Mr Harding said this suggests schools are worried about their national standards' figures.
He said the Government needs to stop publishing individual schools' results.
More about the impact of the national standards can be heard on Insight on Sunday.