This quasi-experimental study examined the short-term effectiveness of Dutch Cell Dogs (DCD), a short prison-based dogtraining program, on anti-social behavioral and wellbeing outcomes of incarcerated adults (n = 138; men = 133; women = 5). Little is known about the responsivity of subgroupsand the prerequisites of changein dog-training programs (DTPs). Therefore, the role of moderators (age, cultural background, correctional facility type) and predictors (dog bond, implementation process) of DCD was also assessed. Results demonstrated that DCD (n = 70) did not outperform treatment-asusual (TAU; n = 68) in any of the outcomes, although a small negative effect was found for aggression (F (1,135) = 5.552, p = 0.020), which appeared driven by the group of participants who had a weaker bond with the dog. This group had higher aggression levels after the program, compared with TAU (F (1, 98) = 9.443, p = 0.003). The dog bond was not associated with any other outcomes post-intervention. In addition, age moderated program effectiveness on infractions (Wald χ 2(1) = 6.254, p = 0.012), suggesting differential effects for younger (< 36 years) participants. No evidence was found for the other moderators and predictor of implementation quality. In conclusion, DCD did not outperform TAU in anti-social behavioral and wellbeing outcomes. Some evidence for predictors and moderators were found. The present study is only one of the first to examine what matters for whom in a DTP for incarcerated adults. More research, preferably in the form of randomized controlled trials with sufficiently large sample sizes, is needed.