The being together intervention intends to raise teacher capacity in Norwegian Early Childhood Education and Care (ECEC) institutions and promote social and emotional development in preschoolers by implementing an authoritative (warm and predictable) adult style in the institution. An authoritative adult balances between building up high quality interactions with children, while at the same time having a predictable structure with clear norms and social expectations in the learning environment. The purpose of this study was to investigate what helped the ECEC institutions to successfully implement the program principles and core components, and what were the challenges. The staff groups of seven Norwegian ECEC institutions in different municipalities who took part in the innovation were interviewed at the beginning and before the end of the first year of implementation. Data analysis identified five success criteria in the implementation process; strong commitment to the authoritative adult style, strong focus on the implementation process, advanced support systems, highly involved leaders, and a collective orientation. These elements resulted in a shared vision and an academically grounded practice in the ECEC institutions. Staff members without formal professional training and a lack of written documentation in the ECEC institutions should be given more consideration in further improvement of the capacity building.