The overall aim of this study is to investigate the effect of school-related factors and early learning experiences on mathematics achievement. In this causal-comparative research, HLM analysis was performed on the data of 6378 students, their parents, and 241 school principals and primary school teachers. As a result of the HLM analysis, at the student level, learning resources at home, parent-child communication on homework/assignments, parent-child activities in early learning years, and the skills acquired during these years were found to have statistically significant effects on the mathematics academic achievement scores of primary school students. At the school level, on the other hand, the socioeconomic structure of the school, the importance that the school attaches to mathematics academic achievement and teachers' perceptions about it, teachers' experiences, and a safe and disciplined school environment have significant effects. These results indicate the importance of early learning experiences especially in the development of the academic performance of primary school students.