The less pupils use computers at school and at home, the better they do in international tests of literacy and maths, the largest study of its kind says today.
The findings raise questions over the Government's decision, announced by Gordon Brown in the Budget last week, to spend another £1.5 billion on school computers, in addition to the £2.5 billion it has already spent.
Mr Brown said: "The teaching and educational revolution is no longer blackboards and chalk, it is computers and electronic whiteboards."
However, the study, published by the Royal Economic Society, said: "Despite numerous claims by politicians and software vendors to the contrary, the evidence so far suggests that computer use in schools does not seem to contribute substantially to students' learning of basic skills such as maths or reading."
Indeed, the more pupils used computers, the worse they performed, said Thomas Fuchs and Ludger Wossmann of Munich University.
Their report also noted that being able to use a computer at work - one of the justifications for devoting so much teaching time to ICT (information and communications technology) - had no greater impact on employability or wage levels than being able to use a telephone or a pencil.
The researchers analysed the achievements and home backgrounds of 100,000 15-year-olds in 31 countries taking part in the Pisa (Programme for International Student Assessment) study in 2000 for the Organisation for Economic Co-operation and Development.
Pisa, to the British and many other governments' satisfaction, claimed that the more pupils used computers the better they did. It even suggested those with more than one computer at home were a year ahead of those who had none.
The study found this conclusion "highly misleading" because computer availability at home is linked to other family-background characteristics, in the same way computer availability at school is strongly linked to availability of other resources.
Once those influences were eliminated, the relationship between use of computers and performance in maths and literacy tests was reduced to zero, showing how "careless interpretations can lead to patently false conclusions".
The more access pupils had to computers at home, the lower they scored in tests, partly because they diverted attention from homework.
Pupils tended to do worse in schools generously equipped with computers, apparently because computerised instruction replaced more effective forms of teaching.
The Government says computers are the key to "personalised learning" and computers should be "embedded" in the teaching of every subject.
Ruth Kelly, the Education Secretary, has said: "We must move the thinking about ICT from being an add-on to being an integral part of the way we teach and learn."
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"Be a scribe! Your body will be sleek, your hand will be soft. You are one who sits grandly in your house; your servants answer speedily; beer is poured copiously; all who see you rejoice in good cheer. Happy is the heart of him who writes; he is young each day."
--Ptahhotep, Vizier to Isesi,
Fifth Egyptian Dynasty, 2300 BC