Background: Cooperation between parents and school nurses is essential for the successful completion of school courses and a healthy school life for children with long-term conditions. Therefore, this study aimed to develop and test a scale to measure parental perceptions of partnerships between school nurses and parents in the school health care (SHC) system for children with type 1 diabetes (T1D). Methods: The content validity, factorial structure validity, convergent validity, discriminant validity, known-group validity, internal consistency reliability, and test-retest reliability of the School Healthcare Partnership Scale for Parents (SHCPS-P) were evaluated. Data were analyzed by performing exploratory factor analysis (EFA), Pearson’s correlation, Cronbach’s α, and independent t-tests. The total sample included 155 parents for the EFA and 49 parents for the stability test. Seventeen items, grouped into 3 dimensions, were extracted through principal axis factoring. Results: The total variance explained by these factors was 53.57%. The scale demonstrated a high correlation with parental satisfaction regarding school nursing and a moderate correlation with diabetes-related safety, thereby showing convergent validity. A low correlation with empathy demonstrated discriminant validity. A significant difference existed in the partnership scores in known-group comparisons. Cronbach’s α was 0.95, and the test-retest correlation coefficient was 0.95, which showed reliability. Conclusions: This study suggests that the SHCPS-P is a reliable and valid tool for measuring the perception of SHC partnership among parents of children with T1D and can be used as an indicator to measure parents’ perspectives about SHC.