Depression during adolescence represents a significant public health concern. It is estimated that up to 20% of adolescents experience an episode of depression that interferes with academic and social functioning and is associated with an increased risk for self-harm. Although significant progress has been made in the last decade in treating mental health problems in young people, effective treatment of depression has been harder to demonstrate. In this paper, we describe the application of a promising evidence-based treatment for adult depression, behavioral activation (BA), to the treatment of depressed adolescents. We briefly present the history and overview of the standard BA approach to adult depression and discuss the rationale for the extension of this approach to adolescent depression. We then focus in detail on the process of adapting the treatment to be adolescent-specific by presenting an early client whom we treated without success. The paper closes with a discussion of lessons learned from our experience of treatment failure, including the need to (a) take a more nuanced view of rumination with a focus on shaping brooding into reflective problem solving, (b) maintain a structured but flexible approach that allows for early introduction of treatment skills most relevant to the individual adolescent, (c) build in careful tracking of suicide risk, and (d) attend to family engagement. Implications for future research and clinical practice also are addressed.