This grounded theory study examined the perceived effects of a cohort of seven secondary-level teachers earning a reading endorsement in a single-district sponsored professional development program. The researcher collected data through semi-structured personal interviews with the teachers, their principal, and the director of special services for the district. Interviews indicated teachers perceived collegial relationships with cohort members enhanced their learning and instructional implementation. The number of teachers with reading endorsements in the junior high resulted in cohort members training non-cohort members in content-area reading strategies and introducing three-tiered literacy classes at each grade level to every student in grades 6 through 8. The most surprising finding was the strong loyalty cohort members expressed towards the district for meeting their professional development needs. This study identifies aspects of the reading cohort other districts contemplating this model of professional development might consider before implementation. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]