Adaptation of evidence-based interventions by implementers is widespread. Although frequently viewed as departures from fidelity, adaptations may be positive in impact and consistent with fidelity. Research typically catalogs adaptations but rarely includes the implementers' perspectives on adaptation. We report data on individuals implementing an evidence-based teen dating violence prevention curriculum. Key informant interviews (n = 20) and an online focus group (n = 10) addressed reasons for adaptations, adaptation processes and kinds of adaptations. All implementers described making adaptations, which they considered necessary to achieving intended outcomes. Adaptations were tailored to needs of individual students or learning opportunities presented by current events, fine-tuned over repeated applications and shared with colleagues. Adaptations modified both content and delivery and included both planned and in-the-moment changes. Implementers made adaptations to increase student engagement, and to fit students' learning needs, learning style, social maturity and culture. Student engagement served as an indicator that adaptation might be needed and provided feedback about the immediate effects of the adaptation. These findings underscore the value of fidelity assessments that measure participant response, intervention-specific guidance to implementers and evaluation of the impact of adaptations on participant response and intervention outcomes.