This article focuses on the evaluation of a form of intervention with families where there is a risk that a child may be placed in a substitute environment. The program, implemented by the Centre jeunesse de Montréal, was reviewed by evaluators for close to five years. Intervention is characterized by: 1) rapid mobilization of various participants, 2) intensity, and 3) a limited time-frame. Caseworkers are available 24 hours a day, 7 days a week, generally intervene in the family environment, and provide varied therapeutic and technical support. The evaluation focuses on: 1) the characteristics of the families and services, 2) the impact of the program on placement rates and reporting following intervention, and 3) the impact of the program on family functioning and the children's well-being. The discussion suggests ways of alleviating problems in the evaluation of intervention programs in child services.