New research has cast doubt on tests being used by some technology colleges and schools to measure aptitude for specialist subjects.
The report by the National Foundation for Educational Research comes as the Government is set to announce the latest batch of schools to attract extra money by becoming specialist institutions.
The NFER gave aptitude tests to 688 Year 11 pupils at 25 schools shortly after they took their GCSE examinations. The aim was to compare the two sets of results to see whether pupils doing well in the aptitude tests were also successful in their GCSEs.
If the tests were a useful indicator of ability in the subjects being assessed, they ought to have shown a consistent similarity with pupils' achievements in the equivalent GCSE subjects.
The research showed there was a strong correlation between the aptitude tests and science and maths, and that they were also a good indicator of general success in GCSEs.
But there was a very weak link between success in the tests and good results in subjects associated with design and technology. The correlation was particularly weak in information technology.
Professor Michael Barber, dean of new initiatives at London University's Institute of Education, said the report showed tests now being used at many city technology colleges and technology schools were unreliable and more research was needed on measuring aptitude for specialist education. Another report by the Institute of Education and also published by the DFEE suggests that there is little common ground between specialist schools over admissions.
It says the CTCs and technology schools admit more boys than girls and it is not clear how representative they are of their communities.
Professor Barber said: "This research shows that you can't effectively select pupils according to their aptitude for particular subjects using existing tests. What you will actually be measuring is general ability." The Institute of Education report acknowledges that the CTCs are very popular, with many heavily oversubscribed, but suggests that more research should be done to find out why this is.
The aptitude tests used in the research were based on those published by the NFER and used by many schools to select pupils. They covered mechanical, spatial and non-verbal reasoning.
Chris Whetton, assistant director at the NFER and one of the joint authors of the report, said: "The research shows that the tests can be useful for some purposes but schools must consider carefully which outcomes they wish to predict."
City Technology Colleges and Technology Schools: review of admissions procedures at Year 7 by Michael Barber and Bet McCallum and Aptitude Tests and Technology: an investigation of aptitude and its relationship with GCSE scores by Martin Coffey and Chris Whetton are both published by the Department for Education and Employment.