Using data collected from 4329 students in the 2015 iteration of the Trends in Mathematics and Science Study (TIMSS), we explore two mediators for the relationship between socioeconomic status (SES) and TIMSS-results in mathematics among Norwegian fifth graders. First, we explore how the students' motivation and self-concept mediate the relationship between SES and test results. Second, by using parent reported SES resources and the parents' attitudes to school and the tested subjects, we examine how these may constitute a path through which their children's motivation and family SES are related to mathematics achievement. We found that students' self-concept accounted for a small but statistically significant portion of SES effects on achievement. Intrinsic motivation did not mediate any of the SES effects on achievement, nor did parental attitudes account for any of the association between SES and motivation or achievement.