It is well documented that elementary school children do not participate in recommended amounts of physical activity, and that elementary physical education programs, even when taught by physical education specialists, generally are unable to insure that children engage in appropriate amounts of activity. One solution to this dilemma is to increase children’s activity levels both in and out of school through collaborative efforts such as whole school programs involving the teachers, administrators, and pertinent others within the school community. If this approach is to be successful, it is important to investigate ways that elementary classroom teachers can be actively involved in school level programs that will ultimately increase children’s physical activity levels. Elementary classroom teachers are often responsible for at least a portion of the instructional requirements in physical education, but tend to view this responsibility negatively. Self-efficacy is a powerful theoretical approach for determining and improving a person’s participatory behavior. This study is an initial attempt to investigate self-efficacy as a framework to facilitate the involvement of classroom teachers in whole school physical activity programs. The purpose was to investigate teachers’ perceptions of their efficacy levels with regards to increasing children’s activity. An instrument was adapted from a previously validated scale, modifying 53 closed-ended items to be specific for this study. Subscales were designed to assess sources of information about efficacy (mastery experiences, vicarious experiences, verbal persuasion, and physiological and affective states), and strength of beliefs in individual and collective efficacy. The instrument also included a series of open-ended responses that encouraged teachers to explain their confidence levels and beliefs relevant to increasing children’s activity levels. A total of 72 elementary teachers completed the instrument. Relationships between the variables were assessed using simple correlations, and multiple regression was used to determine which sources of information were predictors of strength of efficacy beliefs. Open-ended responses were analyzed inductively. A pattern of positive correlations was evident between the sources of information and the strength of beliefs. Physiological and affective states predicted the strength of individual efficacy while verbal persuasion predicted strength of collective efficacy. Personal enthusiasm and investment in a program, and contextual time availability emerged in the analysis of open-ended responses as influential factors in the teachers’ capacity to affect activity levels. The results provide valuable information about how to design meaningful interventions to increase children’s physical activity levels using a whole school approach. Keyword(s): elementary education, physical activity