The purpose of this study was to investigate participating teachers' (PTs) perceptions on the effectiveness of collaborating with a peer for purposes of professional development. As the primary researcher, I wanted to investigate how my colleagues (PTs) perceived peer-to-peer collaboration as a method of professional development. As well, I wanted to investigate the PTs perceptions of my role as a peer. An action research model was used to collect, organize, analyze, and interpret data. The data for the study included interviews, observations, and reflective journals. By making my teaching practice the subject of research, I was able to critically examine it and define my role as a "Collaborative Teacher". The following questions guided the research: (a) What were the participating teachers' (PTs) perceptions of the value of collaborating with a peer? (b) What were the participating teachers' (PTs) perceptions regarding the value of the teacher as mentor, the teacher as coach, and the teacher as leader for professional development? (c) What was the impact of peer-to-peer collaboration on the participating teachers' (PTs) vocabulary instruction? The major finding in this study was that the PTs perceived value in utilizing support provided by me, in the role of a "Collaborative Teacher". This study supports the premise that the use of peer-to-peer collaboration will benefit teachers in the area of professional development by meeting their current instructional needs. Analysis of the data revealed that the two collaborating teachers and I perceived a "Collaborative Teacher" as a combination of roles that encompass a teacher leader as collaborator, action researcher, reflective practitioner, and learner advocate as defined by Erkens (2008). In sub-question one, data revealed the PTs perceived for peer-to-peer collaboration to be valuable it must include a peer's desire for a strong professional development need and communication of the need. It also revealed that teachers need people they trust (relationship building). Teachers need a low stress environment that is conducive for risk taking. Teachers like to collaborate with others who have an unselfish commitment to each other's success (as well an attitude and a willingness to learn). And finally, teachers need to value the expertise and experience the peer brings into the collaboration. In sub-question two, data revealed the value of a teacher as mentor, coach, and leader for professional development as important. The PTs desired more opportunities for peer-to-peer collaboration as a method of professional development. Ultimately, the role of "Collaborative Teacher" best defined my support and interactions with my peers. In sub-question three, data revealed that the PTs were positively impacted with peer-to-peer collaboration in regards to vocabulary instruction. There was an impact on the PTs awareness of the importance for direct vocabulary instruction and the PTs reflections via their reflective journals combined with peer-to-peer collaboration led to a positive impact on vocabulary instruction. Implications of the study include the following: (a) It is likely that the participants of this research will continue being "Collaborative Teachers"; (b) Effective collaboration in peer-to-peer mode that addresses a teacher's need to grow and learn in a non-threatening environment will likely support professional development; and (c) My role of "Collaborative Teacher" will continue to enhance the effectiveness of my teaching as I integrate myself into the currently scheduled collaborative times of my peers. This will allow me to extend relationship building, be a part of critical conversations, share knowledge, gain trust, and make myself available for future collaborative action research projects. [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.]