Using a cluster randomized field trial, the present study tested whether 2 relevance interventions affected students’ value beliefs, self-concept, and effort in math differently depending on family background (socioeconomic status, family interest (FI), and parental utility value). Eighty-two classrooms were randomly assigned to either 1 of 2 intervention conditions or a control group. Data from 1,916 students (Mage = 14.62, SDage = 0.47) and their predominantly Caucasian middle-class parents were obtained via separate questionnaires. Multilevel regression analyses with cross-level interactions were used to investigate differential intervention effects on students’ motivational beliefs 6 weeks and 5 months after the intervention. Socioeconomic status, FI, and parental utility values were investigated as moderators of the intervention effects. The intervention conditions were especially effective in promoting students’ utility, attainment, intrinsic value beliefs, and effort 5 months after the intervention for students whose parents reported lower levels of math interest. Furthermore, students whose parents reported low math utility values especially profited in terms of their utility and attainment math values 5 months after the intervention. No systematic differential intervention effects were found for socioeconomic status. These results highlight the effectiveness of relevance interventions in decreasing motivational gaps between students from families with fewer or more motivational resources. Findings point to the substantial importance of motivational family resources, which have been neglected in previous research.