First published in 1998. One of the most characteristic patterns of recent English penal policy is the rapid spread of detention centres. Any new development of this kind makes it necessary to examine the possible effects of the new measures and to test by reliable methods of criminological research whether the new forms of treatment have led to the desired results. This is particularly so with methods of treatment for which there is no previous parallel. It was from such a proposition that the present study of senior detention centres was undertaken. This study of a senior centre was based entirely on records available at the centre and on evidence of reconvictions obtained from the police and the military authorities. The two centres chosen for the experiment were Werrington House, near Stoke-on-Trent, and Aylesbury Centre, which was adapted for use as a detention centre after the girl's borstal and women's prison had been removed elsewhere.