A study of 11 year olds found that those who had taken 11-plus exams to win grammar school places rapidly lost interest in their school work.

Another group of children, who did not take the tests, were not affected in the same way.

The study was led by Dr Richard Remedios, from Stirling University.

"He said: "What I'm wondering is, as students are doing better and better are they maintaining their interest in their subjects or are we losing that?

"I think this is something important that those involved in education should take notice of."

Worried

The study involved children from Northern Ireland, where children can sit a transfer test similar to the English 11-plus.

A total of 66 children took the test, while another 42 did not. The second group took their normal end of term exams.

Dr Remedios said the transfer test group were "really worried and nervous" before sitting the exam.

"There was the implication that these kids were under a lot of pressure," he said.

The researchers measured the children's motivation in science, English and maths by asking them a number of questions, such as whether a subject was fun or boring.

Before the exams the children all appeared very motivated, but once the exams were over, that changed, Dr Remedios told the British Psychological Society's annual conference in Bournemouth.

Motivation among the transfer test group went down, while it stayed the same among the other group.

He said more research was needed to determine how long the effect would last.

But it was possible that it could put a child off a subject for life.

The Burns report into the education system of Northern Ireland called for an end to the 11-plus and the issue was put out for consultation.

Before devolution was suspended in Northern Ireland last October, the Minister for Education, Martin McGuinness, said the final 11-plus transfer test would be in November 2004.

His successor among direct rule ministers, Jane Kennedy, says she will aim to do that, but cannot promise to stick to that deadline.