The purpose of this study was to explore the effects and impact of interdisciplinary teaming on teacher practices and efficacy. This study revealed the perspectives of eight 7th and 8th grade teachers, who teach one of the core disciplines (English Language Arts, Mathematics, Science, and Social Studies) and the school principal by interviewing them for this case study in an Essential Elements School-to-Watch in Nassau County, New York. It included perceptions from the other 7th and 8th grade teachers on interdisciplinary teams through focus groups and observations during team meetings. Document analysis was performed on artifacts that were collected during the observations. Data were triangulated in order to reveal emerging and prevalent themes regarding the perceptions of teachers about interdisciplinary teaming. There is a need to explore effective interdisciplinary teaming and its effect and impact on teaching practices and teacher efficacy in a middle school environment. Proponents suggest that teachers on interdisciplinary teams in middle schools will have a strong sense of belonging and that their teaching practices will be changed and influenced by each other. In addition, teachers and students feel part of this small community team, which will lead to success for both groups. The National Forum, National Association of Middle Schools, and Essential Elements Schools-to-Watch believe that interdisciplinary teaming is a middle school best practice. Therefore, this study explored the impact of different factors that contribute to a successful interdisciplinary team that emerge through the teachers' perceptions regarding practices and efficacy. [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.]