Background and aims: This study focuses on individual differences in the math competencies of primary-school children in Germany. It considers whether or not there are Matthew or compensatory effects in math literacy and which factors and background characteristics of primary-school children can affect competence development. Despite the abundant research on this topic, the findings are often ambiguous, and studies in the German context are sparse. Sample and methods: We used the Starting Cohort 2 of the German National Educational Panel Study and a weighted multilevel mixed-effects panel regression for our analyses (N = 4,982). Results: Our results revealed compensatory effects for low-achieving students in math literacy. There were also small gender differences, but lower achieving girls can close the gap with boys during primary school. With respect to the educational background of the parents, almost no longitudinal effects were observed. Conclusions: The results indicated that the joint primary-school period has a compensatory effect on lower performing students. However, higher achieving students retained their lead, implying that social inequalities persist to some extent.