Despite widespread recognition of schools\u27 role in the healthy development of youth, surprisingly little research has examined the relationships between schools\u27 overall functioning and the health‐related behavior of students. School functioning could become an important predictor of students\u27 health‐related behavior and may be amenable to intervention. This paper describes the development and testing of the School Functioning Index (SFI) as a first step in investigating this question. The index was developed for use with middle schools and conceived as a predictor of students\u27 violent behavior, with the potential for extending research applications to additional health and social behaviors. Using social cognitive theory, social ecological theory, and social disorganization theory as guides, three domains were identified to operationalize school functioning and identify candidate SFI items: 1) resources available to the school and students; 2) stability of the school population; and 3) the schools\u27 performance as a socializing agent for students. Data for candidate SFI items were collected from public archives and directly from 16 middle schools participating in a school‐based dietary intervention study. Data collection from schools, particularly concerning student aggressive behavior and disciplinary actions, presented challenges. The final SFI comprised nine items and demonstrated good internal consistency and variability. The SFI was modestly correlated in expected directions with violence and other health behaviors. This work supports the feasibility of combining multiple school‐level indicators to create a measure of overall school functioning. Further investigation of validity and more acceptable data collection methods are warranted
