David Hart, general secretary of the National Association of Head Teachers, yesterday accused the manufacturers of Pokemon cards of using sales tactics which trade on children's obsessions.
The craze of collecting the cards, which depict fantasy monsters, has swept Britain's playgrounds, generating sales of £140m in the past six months.
Some of the rarer cards have been changing hands in schoolyards for £25 each.
Many schools have banned the cards after instances of bullying among children trying to obtain the rarer cards.
Mr Hart accused the company of restricting the number of rare cards issued. Speaking on Radio 4's The World At One, he said: "What is happening is the people who are marketing them are holding certain cards so they become rarer and rarer.
"I gather 151 cards make up the set. Children appear to be willing to do all sorts of things in order to get hold of them.
"I actually think they are acting irresponsibly in terms of their marketing. I think manufacturers are trading on the children's obsessions."
In the past few weeks there have been a number of alarming cases where youngsters have been mugged for their Pokemon cards. In one incident in Hull at the weekend, two children aged 12 and eight were robbed at knifepoint by two older boys. A similar attack in Ramsgate, Kent, saw two teenagers attacked by a gang of six youths in a dispute over cards.
The attacks have led police to warn parents of the dangers of allowing their children to carry valuable cards around with them.
Mr Hart said teachers were having to cope with the more sinister consequences of this latest craze.
He suggested the price of the cards was also a factor in the recent spate of attacks. A starter pack of 60 cards retails at £7.25.
Mr Hart said: "They are just outside the sort of money that a child might get for pocket money and that is leading to children fighting each other for them and these extreme incidents such as knifing and stabbing of young children."
But a spokesperson for Wizards of Coast UK, the manufacturers, defended the craze as an aid to social interaction.
The company expressed "extreme concern" at the attacks and in response has set up a Pokemon trading card game league which it claims provides a "controlled, supervised environment for children to play, collect and swap cards".
The Pokemon phenomenon began life four years ago as a Japanese electronic game. Since then it has boomed into a multi-million pound empire boasting collectors' cards, computer games, soft toys and plastic figures.