Experts say it is extremely unlikely mobile phone radio waves could help children think more clearly.
Experts say children should still restrict their use of mobiles
The claim had been made by David Butler, head of the National Confederation of Parent Teacher Associations.
He told a meeting at the Lib Dem conference in Bournemouth, hosted by the mobile phone company O2, heat from handsets could boost children's brains.
The National Radiological Protection Board led the criticism of Mr Butler's claims, saying while handsets did have a tiny heating effect, it was unlikely to be of any benefit.
The claims also contradict government advice, which says children should use mobiles as little as possible.
It seems likely that a small amount of heating happens, but it's unlikely there would be a significant amount of enhancement
Dr Zenon Sieniewicz, National Radiological Protection Board
The mobile phone industry has also carried out extensive research into the safety of handsets and is adamant there is no link between usage and ill health.
And the respected Stewart report, commissioned by the government on mobile phone safety, concluded there were no health risks.
But the report did take a precautionary approach, recommending children should only use mobiles in emergencies because of the theory that they could be more at risk from the radio waves because their brains are still developing and their skulls are thinner.
'Weigh up evidence'
David Butler told the conference fringe meeting: "From a perspective of pupil performance it can enhance things, because that
heating effect actually improves the neuron transfers between neural pathways, and therefore your thinking ability goes up.
He said he had been told of the evidence by a British professor. But he would not identify the scientist.
He stressed the information was "anecdotal" but added: "I have yet to see there is actually evidence that that would create a health problem.
"But I mean, even frankly if there was, I would still be wanting to weigh up what someone was telling me about a health problem against the other benefits that that technology was giving.
"What I am saying is that any parent has to weigh up what is perceived to be the risk in any situation, and then use whatever means they feel appropriate to
minimise that risk.
"I personally have not seen any piece of paper that says to me there is a health risk, which would give me concern."
But Dr Zenon Sieniewicz, science officer for the National Radiological Protection Board (NPRB): "Mobile phones do undoubtedly have a heating effects, but it's been measured at a fraction of one per cent."
He added: "Some early studies did show a slight increase in reaction time in cognitive tests. These could be detected in the laboratory, but probably not in real life.
"And later studies have shown a smaller effect, or no effect at all.
"It seems likely that a small amount of heating happens, but it's unlikely there would be a significant amount of enhancement."
Dr Sieniewicz said children should continue to abide by the precautionary advice, and use their phones as little as possible.
Christine Mangat, joint co-ordinator of Mast Action UK, said she recognised that there had been claims which
suggested that thermal heating, effectively exposure to microwaves, improves reactions and responses.
But she added: "Mr Butler is cherry-picking a bit of information when there is a whole mass of information that would be contradictory.
"It is not recommended that young children do use mobile phones. Under the age of eight, their brain is still developing."