The Challenging Horizons After School Program is one of the only psychosocial interventions developed specifically for adolescents with attention-deficit/hyperactivity disorder (ADHD) that has demonstrated efficacy in multiple randomized controlled trials. To date, however, all research with the intervention has evaluated outcomes at the group level, and it is unclear whether all adolescents respond similarly, or if the intervention is particularly well suited for certain adolescents with ADHD. This type of information is needed to guide stakeholders in making informed choices as part of dissemination and implementation efforts. The purpose of this study was to evaluate trajectories of response to intervention for a large sample of middle-school age adolescents with ADHD (grades 6–8) who received the after-school intervention (N = 112). An additional goal of the study was to evaluate potential predictors of response trajectories, focusing on determining what factors best distinguished between intervention responders and nonresponders. Latent trajectory analyses consistently revealed four or five distinct classes. Depending on the outcome, between 16% and 46% of participants made large improvements, moving into the normal range of functioning, and between 26% and 65% of participants made small or negligible improvements. Multivariate predictor analyses revealed that a strong counselor/adolescent working alliance rated from the adolescent perspective and lower levels of parenting stress and parent-adolescent conflict consistently predicted an increased likelihood of intervention response. Implications of these findings for disseminating the after school intervention and for further intervention development are discussed.