More than 120 children are being mugged every school day, figures compiled by the Conservatives suggest.
Tories say under-reporting means the levels could be even higher
Police figures for England and Wales show 23,698 people aged 11 to 16 were robbed in 2005-06 - or 121 for each of the 195 school days - the party said.
Because official data suggest only a fifth of robberies are reported, the true number could be 604 a day, the Tories added.
The Home Office said it took the issue of robbery "extremely seriously".
The Conservatives compiled the previously unpublished information from requests under the Freedom of Information Act.
Party leader David Cameron said: "We have exposed a huge problem with youth-on-youth crime in this country.
"The figures are staggering with 24,000 robberies on children last year - almost a third of the total in Britain.
"It should not have taken a Freedom of Information request to uncover these figures."
The figures showed victims were among the 11 to 16 age group in 29% of robberies recorded by police last year.
In addition, 40% of alleged offenders were aged 11 to 16, and in some parts of London the recorded annual chance of a child being mugged was as high as one in 20.
A Home Office spokesman said: "The government take the issue of street robbery extremely seriously.
"As a result of concerted action by the police and across government there were 21,000 fewer robberies last year than five years ago."
He added: "The proportion of young people committing an offence remains stable and we have invested significant funds in preventing young people getting involved in crime and anti-social behaviour, including programmes for 13 to 16-year-olds identified at risk of offending, and prevention activities in schools through the Safer Schools Partnership."