The latest TV ad for Shreddies points to the wholegrain carbohydrate content in the cereal and a voiceover claims that "studies show a breakfast like Shreddies helps give kids the mental energy they need to stay involved at school".
An on-screen text also calls the cereal "School Fuel".
Despite complaints from the public who thought it could allude to increased intelligence, or suggest an endorsement by teachers, the UK's Broadcast Advertising Clearance Centre (BACC) said that the basic premise that a daily breakfast like Shreddies helped children concentrate had been accepted by the organisation in 2002.
However the BACC said the ad gave an exaggerated impression of the relevance of 'studies' to the cereal, marketed by Cereal Partners UK.
The BACC said that some of these studies submitted by Cereal Partners merely compared having a breakfast with eating nothing at all at breakfast, which was likely to mislead viewers.
"We believed the viewers would have expected the comparison to be between a range of different types of breakfast rather than between having breakfast or having nothing," said the adjudication, published on the website of the Advertising Standards Authority (www.asa.org.uk).
The ruling is a warning for cereal makers, increasingly promoting the high-fibre content of their products, to make all health claims as transparent as possible.
Cereals have come under advertising authority scrutiny as the government tries to reduce obesity by clamping down on advertising of unhealthy foods to children. Last year an ad for the Kellogg's brand Frosties was hauled up by the ASA for claiming the product was healthy when in fact it is laced with sugar.