Research Findings: Children differ in their ability to adapt to elementary school. Yet, the family factors that foster a successful transition to elementary school are less well understood. Family cohesion as an indicator of a positive emotional climate within families may play an important role for children's ability to adapt to school. Thus, using data from the German National Education Panel Study (NEPS), in a 2-year longitudinal study conducted with a cohort of 357 5 to 7-year-old children and their parents from Germany, we have investigated the role of family cohesion in students' learning-related behaviors and math competency during the transition to elementary school. Results indicated that the relationship between family cohesion in kindergarten and students' second grade math competency was significantly mediated by students' learning-related behaviors in first grade. Results highlight the importance of a positive family climate in early life for the development of children's learning-related behaviors and their later academic success in mathematics. Practice or Policy: Family cohesion is a process-oriented indicator of the family context, which is more malleable than family demographics or socioeconomic status. Therefore, family cohesion might be an important element to consider in intervention programs designed to improve children's early learning-related skills and math competency.