This research study was designed to investigate the impact of constructivist-centered professional development in vocabulary instruction for 14 upper-grade elementary school teachers. The researcher facilitated 10 training sessions held in small groups, during grade level meetings at an urban public school, to develop individual and collective knowledge in teaching students vocabulary strategies. The professional development model included traits of Vygotsky's socio-cultural view of cognitive development and principles of adult learning theory, for an emphasis on collaboration. The nature of the study was qualitative and group and individual case studies were examined with multiple sources of data such as field notes, artifacts, interview questionnaires, and observation tools such as a rubric and a checklist. This study highlights the importance of a learning cycle for teachers to systematically develop students' skills in vocabulary while fostering rich engagement with vocabulary that can address the linguistic diversity that exists in many classrooms today. In addition to shaping a professional learning community, the study revealed that collaborative planning and differentiated learning for teachers are promising approaches for improving knowledge and practice in the field of literacy. [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.]