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Objective: This study measured a variety of within-exposure fear changes and tested the relationship of each with treatment outcomes in exposure therapy. Method: We coded 459 videotaped exposure tasks from 111 participants in 3 clinical trials for pediatric obsessive-compulsive disorder (OCD; POTS trials). Within exposures, fear level was observed continuously and alongside exposure process. Fear change metrics of interest were selected for relevance to mechanistic theory. Fear decreases were classified by function; nonhabituation decreases were associated with observed nonlearning processes (e.g., avoidance), whereas habituation decreases appeared to result from an internal and indirect process. Outcomes were posttreatment change in symptom severity, global improvement, and treatment response. Results: Greater cumulative habituation across treatment was associated with larger reductions in symptom severity, greater global improvement, and increased odds of treatment response. Fear activation, fear variability, and nonhabituation fear decreases did not predict any outcomes. Exploratory analyses examined fear changes during habituation and nonhabituation exposures; higher peak fear during nonhabituation exposures was associated with attenuated global improvement. Conclusions: Habituation is conceptually consistent with multiple mechanistic theories and should continue to be investigated as a practical marker of initial extinction learning and possible moderator of the relationship between fear activation and outcome. Results support the importance of functional and frequent fear measurement during exposures, and discussion considers implications of these findings for future studies aiming to understand learning during exposure and improve exposure delivery.