Millions of American children are taking part in youth fitness testing in their K-12 physical education programs. Despite this investment in time and effort there is virtually no research about fitness testing. The key question of why teachers implement and use fitness tests remains unanswered. This study aimed to identify key factors associated with teachers’ use of fitness tests. Full-time physical education teachers (N = 332) from 10 states participated in the study. The teachers, all of who were fulltime physical educators, were recruited in a number of ways, including soliciting through a national physical education listserve, having teacher educators distribute survey packets to teachers with which they worked, through various school districts, and through personal contacts with teachers. The data were collected through a survey, which was guided by the theoretical model of Ronis, Yates, and Kirscht (1989) for determinants of a repeated behavior (i.e., use of fitness tests in the study). The survey instrument and each section (i.e., demographic information, reasons for using fitness tests, attitudes toward fitness tests) was pilot tested through multiple phases (i.e., two phases of initial pilot testing; final pilot testing that included content validity and construct validity phases using multiple techniques to assess reliability and validity of the scores from the instrument) to ensure acceptable score reliability and validity. The overall attitudes toward fitness tests, grade levels, types of schools (private vs. public schools), gender, age, years of teaching elementary physical education, years of teaching secondary physical education, class size and the association with professional organizations were hypothesized to be the factors that may influence teachers' use of fitness tests. The results of discriminant function analysis, however, suggested that only three variables—overall attitude toward fitness tests, grade level, and the school type—were found to predict fitness test use. More specifically, positive attitudes were associated with greater use of fitness tests. Secondary school teachers tended to use fitness tests more than elementary school teachers. In addition, public school teachers generally implemented fitness tests more often than private school teachers. It was concluded that fitness test use was primarily determined by teachers’ perceptions of fitness tests and their teaching situations, which suggests that attitude and context may be the most important factors in whether and which fitness tests are used.Keyword(s): exercise/fitness, measurement/evaluation, professional development