This paper examines the mediating role of parental literacy and numeracy involvement before the child entered school in the relationship between family socio-economic status (SES) and students’ interest in reading and mathematics. Causal mediation analysis is applied to international assessment data from the Trends in International Mathematics and Science Study-Progress in International Reading Literacy Study 2011 combined study. Results provide weak support for the subject-specific parental cognitive involvement mediating mechanism in the association between family SES and subject-specific interest. In general, the total association with family SES is not strong and the direct role of parental cognitive involvement in students’ interest appears to be more relevant than its role via family SES.