Understanding how to support children from low-income families as they begin kindergarten is paramount, because they may have delays in developing cognitive and social skills in preschool, putting them at risk for poorer outcomes. Importantly, further research needs to be conducted on how specific constructs that relate to school readiness interact, such as inhibitory control (IC) and emotion knowledge (EK). Previous research has examined relations between IC and EK, but the directionality reported is inconsistent, and few studies have the longitudinal data necessary to assess the interaction fully. Thus, the present study (N = 539) aimed to expand previous research by assessing the directionality of the relationship over four time points using cross-lagged panel models in a low-income population. The results showed positive bidirectional relations between the two constructs from preschool to kindergarten, but not kindergarten to first grade, perhaps indicating a shift in these constructs’ interdependency to increased specificity. This study clarified the directionality of these related constructs from preschool into first grade, expanding previous research that focuses on this interaction primarily in the preschool years in samples of convenience. Implications for curricula and intervention for children from low-income families are discussed. (author abstract)