The overall aim of this study is to examine the association between Swedish students’ attitudes towards mathematics, mathematics achievement as measured by the Trends in Mathematics and Science Study (TIMSS), socioeconomic status (SES), and educational background variables. A further aim is to investigate whether students’ attitudes towards mathematics have a mediating role between their mathematics achievement and their background. Several indicators of students’ SES and background, taken from both the TIMSS 2015 database and from Swedish official registers, were used. The overall results show that there were differences in attitudes towards mathematics in relation to the different SES and educational background measures. There are also associations between students’ SES and both TIMSS mathematics achievement and their attitudes towards mathematics. The students’ attitudes towards mathematics only had a small mediation role between the students’ backgrounds and TIMSS mathematics achievement. Finally, although the mediation models had a better fit when including other information, the mediation effect was lower. Practical implications of the obtained results are discussed.