Clever teenagers of today are not as bright as kids in the class of 1976, according to researchers.
The intellect of even the brainiest 14-year-olds has deteriorated dramatically over the decades despite an increase in the number of pupils achieving top grades in exams.
Their cognitive abilities are level with those of 12-year-olds in 1976, the study found.
The tests - designed to assess grasp of abstract scientific concepts such as volume, density, quantity and weight - found far fewer youngsters hit top scores than in 1976.
Professor Michael Shayer, who led the study, said the brainpower slump may be down to over-testing in schools.
He said: "The moment you introduce targets, people will find the most economical strategies to achieve them.
In previous research, Professor Shayer concluded that the cognitive abilities of 11-year-olds were up to three years behind where they were in 1975.
