Low socioeconomic status (SES) is negatively associated with children's cognitive and academic performance, leading to long-term educational and economic disparities. In particular, SES is a powerful predictor of executive function (EF), language ability, and academic achievement. Despite extensive research documenting SES-related differences in these domains, our understanding of the mechanisms underlying these associations and factors that may mitigate these relationships is limited. This systematic review aimed to identify the mediators and moderators in the association of SES with EF, language ability, and academic achievement. Our synthesis revealed stress, support, stimulation, and broader contextual factors at the school- and neighborhood level to be important mediators and protective factors in these associations. In particular, cognitive stimulation mediated the association of SES with EF, language ability, and academic achievement. Educational expectations, classroom and school environment, and teacher-student relationships also played a key role in the association of SES with academic achievement. In addition, factors such as preschool attendance, home learning activities, and parental support buffered the association between low SES and lower cognitive and language outcomes. We discuss these findings in the context of interventions that may help to reduce SES-related cognitive and educational disparities.