This study was a case study of the experiences and perceptions of collaborative, subject-alike planning among middle school teachers. Many investigators have identified gaps between teacher planning and classroom instruction and have asserted that teacher planning often occurs independently and in isolation of other teachers. Researchers in other studies have concluded that collaboration among teachers allows teachers to share experiences and enhances classroom learning. From a constructivist theoretical framework, learning is the result of interactions and deliberate processes by teachers that require students to assimilate knowledge. Key research questions in this study focused on how middle school teachers perceived subject-alike planning to impact classroom instruction and student achievement. Data were gathered from 5 teacher interviews, 2 panel discussions, and 3 observations of teacher planning sessions. Data were coded and common themes were identified based on the theoretical framework. Triangulation of data and member checking ensured the accuracy and credibility of study findings. Findings in this study indicated that participating teachers perceived collaborative planning with subject-alike teachers to improve classroom instruction and increase student mastery of content in their classrooms. Recommendations for administrators include providing quality common planning time for subject-alike teachers that contributes to their professional growth and improves classroom instruction. Results from this study contribute to positive social change by clarifying teacher beliefs and perceptions regarding the effectiveness of collaborative subject specific planning on classroom instruction and student and teacher learning. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]