This article deals with one of the multiple and complex aspects that shapes quality in Early Childhood Education and Care (ECEC), such as teachers' professional development. It presents the successful case of the RIECU Network in Spain in which for almost two decades the following institutions have been cooperating: (1) the university, responsible for initial teacher training, (2) the institution in charge of in-service teacher training and (3) the ECEC centers where professional development takes place through the practical experience of teachers. Data obtained from the focus groups with representatives of the three institutions reveal that the greatest benefit that teachers perceive for their professional development is the interaction, professional contact and shared reflection with their colleagues, and the creation of a stimulating learning environment in which they feel welcomed and valued, moving from a competitive culture, widely spread in their schools, to a collaborative culture conducive to teaching innovation.