ABSTRACT Background Family‐school partnerships (FSPs) play an important role in supporting child health and well‐being. The current study aimed to develop and validate a psychometrically sound instrument to assess FSPs within the context of child health. Methods The instrument was developed through a mixed‐methods three‐phased approach, including pilot testing with 105 parent/caregiver ( n = 53) and school staff ( n = 52) participants. Analytic methods included principal component analysis (PCA) followed by exploratory factor analysis (EFA) that used polychoric correlations. Results Results of the PCA and EFA analyses refined the instrument to 24 items across two factors: communication, engagement, and culture (14‐items), and opportunities and supports for family engagement (10‐items). Implications for School Health Policy and Practice The Family‐School Partnership Assessment (FSPA) offers a validated framework to enhance school health initiatives through improved partnership strategies. The FSPA promotes inclusive practices and structured approaches for collaborative family engagement. Conclusions The FSPA is a feasible and psychometrically valid measure for assessing FSPs within the context of child health.