Aha! As I suspected! See this from Andrew Orlowski:
A study of 100,000 pupils in 31 countries around the world has concluded that using computers makes kids dumb. Avoiding PCs in the classroom and at home improved the literacy and numeracy of the children studied. The UK’s Royal Economic Society finds no ground for the correlation that politicans make between IT use and education.
The authors, Thomas Fuchs and Ludger Woessmann of Munich University, used the PISA tests to measure the skills of 100,000 15 year-olds. When social factors were taken into account, PC literacy was no more valuable than ability to use a telephone or the internet, the study discovered.
“Holding other family characteristics constant, students perform significantly worse if they have computers at home,” the authors conclude. By contrast, children with access to 500 books in their homes performed better.