Police have investigated an allegation of indecent assault involving young students at an exclusive private boys school on Sydney's north shore.

The school community has been rocked by the claims, which have been reported to the Department of Community Services.

Police called ... year 4 pupils from a private boys school on Sydney's north shore are at the centre of an indecent assault allegation. Credit:Janie Barrett

The Sun-Herald understands that a group of boys in year 4 invented a playground game dubbed ''the humping game''.

The mother of a boy at the school told The Sun-Herald the ''game'' involved two students holding a victim down while a third would pull his pants down and stroke his penis. The targets were generally new students and the perpetrators would warn their victims not to report what happened.