Socioeconomic status (SES) is considered a major predictor of student and school achievement. In most cases, SES is not malleable or available for manipulation to improve students' learning and achievement. Therefore, we explored other student and school-related factors that may be malleable to reduce achievement differences between students and schools in Turkey. We used the TIMSS 2015 fourth-grade mathematics data and analyzed it using hierarchical linear modeling. We found that SES at both student and school levels is a dominant factor related to mathematics achievement and a much stronger predictor at the school level. Early literacy and numeracy activities, preschool education, intrinsic motivation, and engagement in instruction were found to be significantly and positively associated with higher achievement within schools. Similarly, among the school-level variables, we found significant and positive associations between schools' mathematics scores and instruction quality and school readiness, in the presence of SES. We recommend that preschool education and early literacy and numeracy activities at home should be promoted. Additionally, although the findings of this study indicate possible SES-based school segregation; parents, teachers, and school leaders, as well as students, should work toward a more positive school climate to reduce achievement disparities due to SES.