The objectives of the research are to examine: (1) the relationship between parents' education level as an indicator of socioeconomic status (SES) with students' mathematics achievement, and (2) the interaction between parents' education level and the intensity of parental involvement in predicting students' mathematics achievement. The sample (N=2,867) was selected through stratified random sampling of Indonesian high school National Examination (NE) test takers in 2016. The sampling was based on careful consideration of the representativeness and the distribution of provinces, gender, type of school (general-vocational), and school status (public-private). Data was analyzed using parallel multiple mediator analyses. The findings highlight that: (1) compared to fathers, mothers' education level had a stronger contribution to students' achievement in mathematics, and (2) mothers' involvement mediated the relationship between mothers' level of education and students' mathematics achievement. However, more intensive parental involvement was associated with lower mathematics achievement.