Although this guide targets juvenile justice practitioners, it is generally applicable to programs in other social service fields as well. The first section describes an outcome evaluation, which is defined as a formal study that helps to answer the basic question, Is this program working? Its aim is to collect and examine evidence of changes in clients' behavior and, if there are changes, show that they result directly from participants' experience in the program. After defining an outcome evaluation, the guide discusses why an outcome evaluation is needed and how to prepare to conduct an outcome evaluation. The following steps are outlined: determining whether the program is true to its original plan; defining the study group and control group; identifying the sources for the data to be collected and analyzed; and preparing a full report that traces the evaluation steps and describes what was learned about the program.