This research uses in-depth cases studies in five counties, combining interviews and observations, interviews with state reform leaders, and a statewide survey, to examine juvenile probation officers' use of the Youth Level of Service/Case Management Inventory (YLS/CMI) in local practice. In particular, the study assessed the form YLS/CMI policies take in local Pennsylvania counties and their consistency with the Risk-Need-Responsivity (RNR) model, the extent to which officers' routine practices align with policies and RNR principles, and how state and county factors have shaped local policies and practices. In doing so, it sought to highlight promising strategies for effective RNA implementation. Study findings describe an example of an apparently well-planned statewide effort to implement and support the YLS/CMI in local counties, involving a sustained attention to attention to training, quality assurance, and problem-solving. Local county policies, while showing some variation, focused on strategies for conducting the YLS/CMI assessment and applying its results to a variety of decisions and activities--supporting, in particular, risk and need principles. Study results further suggest a substantial statewide level of practitioner adherence to a general policy model, though this pattern was stronger for some activities than others, and varied substantially by local county. Variation in implementation across counties seemed to relate, in particular, to the extent of local quality assurance processes, leadership enthusiasm for the YLS/CMI, staff enthusiasm for evidence-based practices (with implications for training and recruitment), and organizational climate.