According to Birchak, Connor, Crawford, Kahn, Kaser, Turner, & Short (1998), Fang, Fu, & Lamme (2004), Kennedy & Sheil (2010), and Wiliam (2008), teacher study groups can provide a supportive and collaborative professional development environment. The purpose of this study was to examine the professional development experiences of three third grade teachers working with culturally, linguistically, and economically diverse (CLED) students in a high-needs school as they participated in a teacher study group. The adoption of national standards and pressures for all students to achieve high standardized test scores in math and reading due to Adequate Yearly Progress (AYP) requirements mandated by the No Child Left Behind Act (2001) resulted in increased stress, anxiety, and uncertainty for the teachers participating in this study. The following research questions guided this qualitative, ethnographic case study: (1) In what ways does participation in a teacher study group impact elementary teachers' knowledge, beliefs, and understandings when teaching culturally, linguistically, and economically diverse students in a high-needs school? (2) In what ways do teachers' literacy practices shift as a result of engaging in teacher study groups focused on issues related to culturally, linguistically and economically diverse student populations? Bronfenbrenner's (1979; 1994) ecological models, Vygotsky's (1978; 1986) sociocultural theory, and Ruddell and Unrau's (2004) sociocognitive reading model served as theoretical frameworks that informed this naturalistic inquiry. Through constant comparative analysis (Glaser and Strauss, 1967) of data collected through pre- and post-interviews, bi-weekly teacher study group meetings, and classroom observations, the teachers' knowledge, beliefs, and understandings about how culturally, linguistically, and economically diverse (CLED) students learn and develop literacy skills were explored. The findings of this study demonstrate how teacher study groups can provide teachers with a safe space to build trusting relationships so that they can discuss school and classroom-related uncertainties, vulnerabilities, frustrations and successes. Shifts in enacted curriculum, instruction, and beliefs occurred as the teachers in this study attempted to negotiate their beliefs about how CLED children learn through engaging in conversations related to integrated curriculum, higher-order thinking, inquiry-based learning, literacy instruction, literacy development, and the diverse needs of their students. [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/en-US/products/dissertations/individuals.shtml.]