John Dunford says world class tests are an "irrelevant hurdle"

These voluntary tests, expected to be introduced next year, will measure ability in maths and problem -solving and will be aimed at the brightest 10% of pupils.

But Mr Dunford has criticised their introduction as an "irrelevant hurdle" which will "add unnecessarily to the stress levels of academically able children".

The world class tests were "a further example of the government's obsession with testing at the expense of true education", he said.

But the Qualifications and Curriculum Authority (QCA) has rejected the attack, saying the tests would be voluntary and it would be up to schools to decide whether or not they want to use them.

Schools would be able to use the tests to identify and stimulate gifted pupils, and parents would be able to use the tests with their children at home.

The tests have been designed to stretch the most able pupils, and in the future could be used as a benchmark for making international comparisons in standards of maths.

The tests are set to be piloted in a sample of schools in the United States next year.

On Monday, the QCA launched a website illustrating the type of questions which will be asked in the tests.