This study sought to elucidate the contributions of inferior executive function and social competence to the development of internalizing and externalizing problems in primary school. Children (N = 1,115), on average 5.36 years old in first grade, were followed across primary school with measures of multi-method and multi-informant. Results of growth modeling demonstrated that poor executive function in first grade predicted high levels of both problems and a low rate of decline in externalizing problems over time, independent of the co-occurrence of both problems. Moreover, the impact of poor executive function on behavioral problems may be dependent on its association with disruptive social competence. Findings highlighted the interrelations of risk factors to understanding the development of behavioral problems in primary school.