A programme to drug test suspected child offenders is being launched by the Home Office in Manchester later.
Suspects will be tested for crack, heroin and cocaine
From Saturday, children aged 14 to 17 in 10 pilot areas of England will be tested for cocaine, heroin and crack when charged with property crimes.
Home Office Minister Caroline Flint will also release the results of a similar programme for adult suspects, which was launched in October 2001.
Those who test positive for the Class A drugs are offered voluntary treatment.
Child testing pilot areas
In May, 48% of those adults tested gave a positive result - a quarter were persistent offenders.
A Home Office spokeswoman said: "Evaluation results show that drug testing, while it does not reduce the number of people taking Class A drugs, does highlight those who are and enables them to get treatment."
Ms Flint will launch the child testing scheme at Manchester's Drug and Alcohol Action Team.