Background: In Japan, school health examinations frequently utilize growth curves. This study aimed to develop and validate a custom-designed program that enables the rapid and accurate detection of growth abnormalities in children and adolescents. Methods: We created a novel screening tool named the Growth Assessment Program for Schools (GAPS), implemented using Visual Basic for Applications (VBA) in Microsoft Excel. Using the 2021 school health checkup data (IZUMO 2021; 12,573 students, aged 6-15 years) from Izumo City, we validated the program's accuracy against both the frequently used abnormal growth curve determination program (V4) and an expert review committee. Results: The GAPS tool enables one-click generation of individualized growth curves and automated identification of abnormal patterns. It successfully detected growth disorders, including cases such as precocious puberty, that were initially overlooked by tV4 (341 cases, 2.9%). Compared to V4, the GAPS tool demonstrated improved sensitivity (0.99) and positive predictive value (0.16), though with a higher false positive rate (0.24). Implications for School Health Policy, Practice, and Equity: GAPS allows for immediate application by school personnel, including non-specialist school physicians, enabling real-time health surveillance and improving the quality of school-based pediatric care. Conclusion: We developed and validated GAPS, a user-friendly and highly efficient tool for detecting abnormal growth curves in school health settings in Japan. It offers advantages in speed, accuracy, and usability over existing programs. This program also holds potential use in broader populations, provided population-specific growth data are available.