This study is a survey that was intended to measure the connection between what co-teachers actually do and what they think they should be doing as best practice. Second, it intended to study the roles and responsibilities that co-teachers report fulfilling. Finally, whether self-efficacy is a predictor of co-teacher roles and responsibilities is further reported. Three hundred twenty co-teachers participated in the study: one hundred sixty special education and 160 general education teachers in a large urban school district in the southwestern United States. Bandura's Teacher Self Efficacy Scale (1994) was used with a tool for co-teachers designed specifically for this study. Results of this study indicate that co-teachers, general education and special education, reported executing fewer roles than what they considered best practice. Both general and special educators reported engaging in different tasks than their co-teaching partners in the areas of co-instruction, co-planning, and co-behavior management. Co-teachers who reported having greater self-efficacy were, according to the survey results, more likely to plan and differentiate together. [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.]