The present study is based on longitudinal data from a German early childhood education and care (ECEC) governmental initiative assessing children's grammatical and vocabulary development between 2;6 and 4;0 years (N = 1,331), quality of the home learning environment and quality of the preschool setting. Results showed that the quality of the home learning environment predicted development in grammatical skills, but not in receptive vocabulary at age 4, while the effects of preschool process quality showed similar relative impacts on both language outcomes. Further analyses revealed effects of accumulated advantages of preschool quality for children from medium- and high-quality home learning environments in their vocabulary development. The results are compared with previous findings from the German ECEC context and discussed with respect to implications for policy efforts to improve ECEC quality and ways in which both learning environments act together on children's development.