Despite the fact that research shows that collaboration between families and schools contribute to academic achievement, social-emotional development and sense of well-being of students, many schools struggle to establish family-school partnerships. The current study explores keys to success and challenges in engaging families to the design and implementation of School Wide Positive Behavioral Interventions and Supports (SWPBIS). In a two-step systematic assessment, consisting of an online survey (n = 27 participants) and five focus group interviews with administrators and members of SWPBIS leadership teams in schools for primary education (n = 15 participants), we found that all 27 participating schools considered partnerships and communication with parents important. However, most participating schools did not have a policy or strategic planning for engaging families, nor did they systematically evaluate their actions. Schools used one-way approaches of communicating with parents and found it hard to adapt their communication to a diverse population of new parents and parents already familiar with SWPBIS. Schools did not communicate about what was achieved by implementing SWPBIS in their school. Including families in the SWPBIS leadership team was often considered challenging. Input from families on SWPBIS was not collected, nor did schools gather information about family's needs, (cultural) backgrounds to develop strategies for engaging families. Further research on actual school practices in engaging families is recommended.