Background: Transition to school is a highly demanding phase at an intellectual, social and emotional level and is, therefore, an opportunity for growth and development. Despite the greater emphasis given to school transition in Portugal over recent years, namely by means of new educational policies, studies on the adaptation processes involved in the transition to primary school are still scarce. Purpose: The present qualitative study sets out to contribute to the knowledge on the adaptation process of children to school transition (around age 6) in Portugal, by comparing preschool teachers', primary school teachers', and parents' perceptions about success indicators and relevant factors in the transition to school. Design and method: In order to collect data, 14 focus group interviews with different participants were conducted, three with preschool teachers (N = 18), three with primary school teachers (N = 13), four with parents conducted before the child's transition to primary school (N = 14) and four with parents conducted after the child's transition to primary school (N = 20). Results: While the preschool and primary school teachers stressed factors of a family nature, such as parental involvement and parental support of children, the parents referred more frequently to the overall running of the school and the characteristics and methodology of the teacher as being relevant to the adaptation process in the first year of primary education. Conclusions: The findings suggest different factors associated with adaptation to school and also offer clues for designing strategies to facilitate such adaptation. New strategies are needed to facilitate the construction of a robust educational family-school partnership.