This qualitative case study examined teachers' perceptions of fourth-grade departmentalized science instruction at Title I schools. Three theoretical frameworks were used as a lens for the study: Model of School Learning (Carroll, 1963), Theory of Mastery Learning (Bloom, 1968) and Curriculum Ideologies (Schiro, 1992). The three theories were used to examine four research questions, which were: What are fourth-grade teachers' perceptions or curriculum ideologies about departmentalized science instruction at Title I schools? How does departmentalized science instruction shape the curriculum ideologies of fourth-grade teachers in Title I schools? How does fourth-grade departmentalized science instruction shape the teaching process at Title I schools? How does fourth-grade departmentalized science instruction shape the learning process at Title I schools? For this qualitative case study, six teachers who taught fourth-grade departmentalized science at four Title I schools were interviewed during one-on-one interview sessions, and three instructional coaches who provided instructional support to teachers were interviewed during one-on-one interview sessions. Teachers who taught fourth-grade departmentalized science at four Title I schools were also recruited to participate in two separate focus group interviews. Additionally, documents such as fourth-grade class schedules and science lesson plans were reviewed. The findings from the study indicated that teaching fourth-grade departmentalized science in Title I schools did shape the teaching and learning process for both students and teachers in various ways. On the contrary, findings from the study did not indicate that teachers' curriculum ideologies were shaped by teaching fourth-grade departmentalized science in Title I schools. The findings from the study can be used by district leaders, school administrators, teachers, and instructional coaches to influence organizational structure decision making for Title I schools. This study is significant because it adds to the body of knowledge about departmentalized science instruction for students enrolled in Title I schools. [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.]