The slippery tale of how fish oil can boost exam results and banish bad behaviour has wriggled its way back into the headlines.

The latest twist involves an Australian study which claims that a combination of fish and evening primrose oils is more effective than drugs such as Ritalin in tackling attention deficit hyperactivity disorder (ADHD).

The study, by the University of South Australia, found that 30 per cent of seven to 12 year-olds who took a food supplement containing the oils were considered by their parents to have become less hyperactive.

The study, which involved 132 children, was funded by the university and a young people’s charity, and free fish oil was provided by food firm Equazen. One group of children took a placebo, containing no active ingredients.

Earlier this month the Food Standards Authority admitted launching a review by Teesside university of existing studies on the link between Omega 3, the fatty acid in fish oil, and improvements in the classroom.

However, a leading academic has questioned the value of most of the studies being reviewed. “The vast majority cannot be described as scientific research,” said Dr Alex Richardson, a senior research fellow at Oxford University. “Companies approach schools and promise to give out free fish oil if the schools allow plenty of PR. The impression then given is that fish oil is the magic pill which will cure all your children’s ills. I wish someone would point out to the public the difference between a scientific trial and a company advertisement.”

Dr Richardson is trying to raise pound;1 million to fund the first scientific research looking at the benefits of fish oil to mainstream pupils. More than a thousand children would be involved, at around 20 primaries. “The Government should spend a moderate amount of money getting proper research done before spending millions of pounds of taxpayers’

money,” she said.

Baroness Tonge, a Liberal Democrat peer and former doctor, who was pilloried three years ago for asking if the Government would consider giving cod liver oil to children, said: “The idea of teachers dishing out fish oil is nonsense. There is not enough evidence of the benefits. Giving them Smarties might have a similar effect.”

Dr Frankie Phillips, spokeswoman for the British Dietetic Association, added a further note of caution: “Most of the information on the benefits of Omega 3 is quite anecdotal. We would like to see proper scientific trials. There must be a group of children who receive only a placebo.”

Dr Phillips added that there were many other nutritional factors that affected children’s school performance such as dehydration, not eating a proper breakfast and, particularly for teenage girls, a lack of iron.