A new study suggests that, whatever rules teachers make to stem the invasion of the latest fad, ingenious children will always find a way round them. Ban mobiles from school, for example, and pupils revert to passing notes in text-message English. Banish Pokemon cards and children concoct an invisible version of the game - using imaginary cards.

Elizabeth Grugeon, senior lecturer in English in primary education at De Montfort University, Bedford, said: “Children like to cock a snook at authority. Passing notes and inventing languages have always been done. It is part of the subversive nature of play.”

More than 200 of her trainee teachers were involved in a three-year study of playground fads, following the the fluctuating fortunes of Pokemon, Star Wars, Harry Potter and others.

The study reveals the lengths that children will go to to pursue their current obsessions.When mobiles were banned in one school, a trainee teacher discovered children passing paper notes saying “C U 2morrow” or “C U l8r”.

When Pokemon cards were banned, the children simply made their own which became even more popular.

One group of Year 4 boys were inspired to invent “Dragon Cards”, a game played with an imaginary set of cards, with children memorising details of the different characters, Ghost Dragon, Thunder Dragon and Ice Dragon.

The De Montfort study confirms that teachers face an unequal battle for children’s attention with cartoons, films and popular TV programmes .

“Do not denigrate the role of the media in children’s culture,” said Mrs Grugeon. “Computer games and television are such a major part of their life that not acknowledging it can be counterproductive.”