A minister has admitted for the first time that the new testing system being trialled to replace existing key stage tests could add to the assessment burden on pupils.

Lord Adonis, the junior schools minister, told a London conference that the Government was not yet committed to introducing single-level tests, which are expected to replace Sats within three years.

“There are some teachers who passionately believe that single-level tests will help,” he said. “There are those who argue that it simply spreads the national testing burden over a larger number of years.

“It will be my job to take stock before we take any decision on a national roll-out.”

Attending a National Centre for Excellence in the Teaching of Mathematics conference, Lord Adonis heard concerns that the new tests would undermine efforts to improve maths teaching because teachers would concentrate narrowly on exam success.

He said that the advantages of the new system were great: for instance, they would relieve pressure on Year 6 pupils and teachers, and would give children a greater incentive to make progress. But some critics argued they could result in “more testing, not less”, he said.

Single-level tests mean pupils are entered for specific tests when their teachers judge them to be ready. All key stage 2 and 3 pupils are assessed informally by their teachers, then entered for the level the teacher judges to be appropriate. The tests are available twice a year in English and maths. They have been piloted in more than 400 schools in 10 local authorities since last year. The trial continues until 2009. Last week, 36,225 pupils in 446 schools took the second round of trial tests.

Many of those who responded to a consultation on their introduction said they risked extending the testing culture throughout Years 3 to 9.