The gap between service need and service use for youth with behavioral health problems is well documented. Although provider perception of need predicts service access, studies have found low associations between youth report and provider perception. This paper posits that provider perception of functioning mediates the relationship between youth need as measured by symptoms and provider assessment of that need. Interviews concerning service need and use with 792 14-18-year olds, and surveys of 222 of their providers, were analyzed through structural equation models. Functioning mediated the path from symptoms to assessment when contextual variables were not included in the model, but did not explain additional service use. However, when both contextual factors and functioning were included, the path from functioning to assessment was not significant and less service variance was explained (46% vs. 55%) than in a model not including functioning. Functioning may explain the relationship between symptoms and assessment, but organizational and individual provider variables explain service variance.