The goodness-of-fit model, which proposes that developmental outcomes result from combinations of environmental and children's factors, has contributed substantially to the recognition of person × environment processes. However, which pattern of person × environment interactions characterizes this model remains unclear, making it difficult to test or compare with other models (e.g., the differential-susceptibility model). In this article, we offer solutions for these issues. We propose that a contrastive effect pattern best summarizes both goodness of fit and poorness of fit. We outline methodological considerations that help determine whether a person × environment interaction supports the goodness-of-fit model. We then discuss how person × environment interactions can be culturally specific, an issue aligned with the goodness-of-fit model but not other models. We illustrate cultural specificities in socialization-by-temperament interactions with evidence from different sociocultural groups. These theoretical and methodological refinements help clarify how person × environment interactions can be interpreted and predicted by the goodness-of-fit model.