Attendance at preschool represents an important transition, as it is often here that children have their first experience with unfamiliar adults. In this context, several factors can affect children's adjustment. Two important protective factors are the attachment relationship with the teacher and the level of executive functions. We investigate this interaction in order to reduce the occurrence of internalizing and externalizing symptoms. The results show that both the quality of the attachment relationship with the teacher and executive functions are related to a lower occurrence of internalizing and externalizing behaviours, and that executive functions play a mediating role between the attachment to the teacher and children's behaviours. Therefore, from the perspective of promoting children's adjustment to preschool and, more generally, children's well-being, it is critical at this age to promote the development of executive functions within a secure attachment relationship with the preschool teacher.