Children as young as four are re-enacting scenes from ultra-violent video games at school after being given free access to consoles in the home, according to teachers' leaders.
Infants are being allowed to stay up until the early hours playing 18-rated games such as Call of Duty and Grand Theft Auto because of a failure by parents to impose greater controls, it is claimed.
Alison Sherratt, former president of the Association of Teachers and Lecturers, says growing access to "horrific" games is responsible for an increase in the amount of aggressive behaviour in school playgrounds.
In a speech to the union's annual conference on Wednesday, she will say that teachers have witnessed the youngest pupils "acting out quite graphic scenes", including a rise in "hitting, hurting and thumping".
Do video games fuel aggressive behaviour?
Mrs Sherratt, a teacher at Riddlesden St Mary's CofE Primary School in Keighley, West Yorkshire, says her class of four and five-year-olds was seen in the playground "throwing themselves out of the window of the play car in slow motion and acting out blood spurting from their bodies" to mimic scenes from violent games.
She adds: "I began to reflect on what children have been playing over the last few years and realised we have noticed a marked increase in the aggression in general.
Mrs Sherratt says a small-scale survey in her own school suggested almost all pupils had access to TVs, computers and game consoles such as PlayStations, Xboxes and Nintendo Wiis in their bedroom.
She suggests that increased access to screen-based entertainment meant children were arriving at school too tired to concentrate.
"I would suggest that if children are taking part in this fairly solitary existence this will impact on their speaking and listening skills which, in turn, will impact on their ability to concentrate and learn in school," she says.
On Wednesday, the ATL, which represents 160,000 teachers and school support staff, are expected to back a motion calling for the union to commission fresh research into the link between video games and behaviour.