Children's physical inactivity is becoming an important health concern, and it has been suggested by professionals that school programs can be important in the effort to increase activity levels. Physical education specialists cannot achieve the goal of significantly increasing children's activity in isolation, and it is apparent that whole school programs at the elementary level have the potential to foster active lifestyles. If those programs are to be successful, all school personnel must play a role, so it is important to find ways to facilitate their involvement. The purpose of this study was to use collective efficacy as a framework to examine elementary classroom teachers' and principals' perceptions about integrating physical activity into classroom lessons. Participants were 314 elementary teachers and 38 elementary school principals. They completed a survey to assess their physical activity patterns, willingness to integrate physical activity, and role preparedness. Participants also rated the influence of sources of information about efficacy, and the strength of individual and collective efficacy. Based on survey responses, 21 teachers and 12 principals were purposively selected for interviews to represent individuals with high and low efficacy. The interviews focused on their perceptions of barriers and enablers to movement integration. The participants acknowledged the importance of children's physical activity and generally indicated they would be willing to integrate movement into classroom activities to some degree. Willingness to integrate was related to both individual and collective efficacy, but personal involvement in physical activity was not. Although there was a strong relationship between individual and collective efficacy, there was evidence that those variables are distinct and that collective efficacy varied by school context. Mastery experiences were most influential in predicting strength of individual efficacy, while institutional environment was the strongest predictor of collective efficacy. The three themes that emerged from the analysis of the qualitative data reflected the belief that (a) effective management is essential to successfully movement integration, (b) extensive inservice training would be needed, and (c) provision of administrative support and inclusion of physical activity in the accountability system are necessary if teachers are to be committed to integrating movement. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]