Although there are several well used self-efficacy instruments designed to measure PE teachers' self-efficacy to teach students with disabilities, limitations to these scales exits, such as a narrow focus on integrated instructional placements and an absence of theoretically relevant sources of self-efficacy information built within the scales. These limitations translate to a significant gap in the literature between measuring PE teachers' self-efficacy and understanding how sources of self-efficacy information interact to shape PE teachers' self-efficacy beliefs, as well as understanding how different instructional placements may inform efficacy. This dissertation was structured in a two-manuscript approach. The purpose of the first study was to develop and validate a scale designed to measure PE teachers' self-efficacy and sources of information to teach students with disabilities across different types of instructional placements for PE. The scale was constructed in four phases: (a) item development, (b) content validity, (c) exploratory factor analysis, and (d) confirmatory factor analysis. Data from 268 (172 males; 86 females; five others; five undisclosed) and 169 (105 females; 64 males; one undisclosed) participants was used for exploratory factor analyses and confirmatory factor analyses, respectively. The final instrument comprises 29-items including a 7-item (one factor) self-efficacy scale and an 8-item (two factor) efficacy-relevant information subscale for teaching students with disabilities in an integrated PE placement, as well as a 7-item (one factor) self-efficacy scale and 7-item (two factor) efficacy-relevant information subscale for teaching students with disabilities in a self-contained PE placement. The purpose of the second study was to examine the differences in PE teachers' self-efficacy to teach students with disabilities across integrated and self-contained classes as well as the association between efficacy-relevant information and PE teachers' beliefs in their capabilities to teach across each placement. A total of 169 (105 females; 64 males; one undisclosed) in-service PE teachers in the US completed the scale developed in study one as well as a demographic questionnaire. Differences in self-efficacy between placements were tested using analyses of covariance, and associations between variables were explored via structural equation modeling. No significant differences were found between PE teachers' self-efficacy to teach in an integrated placement compared to a self-contained placement. Further, no distinctions in self-efficacy were found among PE teachers with experience teaching in only integrated or self-contained placements. However, those with experiences in both placements reported a slightly higher self-efficacy to teach in a self-contained placement. Favorable efficacy-relevant information was a direct predictor of PE teachers' self-efficacy in both integrated and self-contained classes, however, unfavorable efficacy-relevant information had only an indirect prediction on self-efficacy with favorable efficacy-relevant information serving as a mediator. Further research may consider exploring diverse methodological procedures aiming to further connect the impact of efficacy-relevant information on PE teachers' self-efficacy across instructional placements to extend our understanding of why and how self-efficacy appears consistent across instructional settings. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]