The authors begin by reviewing the scant research available about persistent offenders. Social policies regarding youth crime in Western developed countries is examined followed by a description of the particular policy changes in England and Wales that led to the development of the ISSP. Inter-agency efforts to reduce criminal recidivism among young offenders resulted in ISSP, which targets young offenders with at least three convictions or cautions who are between the ages of 15 to 17 and have experienced custody or a failed community sentence. ISSP involves seven components: (1) joint and frequent supervision by police and social services staff; (2) family group conferencing to identify needs and arrive at solutions; (3) victim reparation and mediation where appropriate; (4) a mentoring scheme involving young volunteers who act as role models and help fill free time constructively; (5) improved assessment, diagnosis, and treatment; (6) improved collaboration between police, social services, and education professionals; and (7) regular multi-agency review of cases. ISSP was evaluated by randomly allocating participants to the experimental (ISSP) group or to two control groups. Four measures were used for evaluation purposes: (1) number of court appearances resulting in conviction during follow-up; (2) number of arrests during follow-up; (3) number of arrests per month of liberty during follow-up; and (4) pre-post arrest offense ratio. Results of statistical analyses indicated that, as hypothesized, ISSP had no impact on reconviction rates. More than four-fifths of participants were reconvicted during follow-up and there was no significant difference between the ISSP group and the control groups. However, the ISSP group was 30 to 50 percent less likely than controls to be arrested during follow-up, despite the increased vigilance of the police toward this group. No single component of the program was associated with successful outcomes, suggesting a possible placebo effect. Improved data about persistent offenders is crucial to driving program design and improving outcomes for this group of hard to reach offenders. Tables, references