This study uses practitioner research to examine secondary mathematics teachers' learning of literacy integration practices in the context of a district-wide literacy professional development series. The author, a secondary mathematics curriculum and instruction facilitator in a large, Midwestern suburban district, engaged in a two-year partnership with seventeen Mathematics Teacher Facilitators (MTFs) who taught literacy practices to their colleagues via a train-the-trainer model. This study provides an explicit rendering of professional development practices and ongoing, job-embedded learning vignettes of six MTF's experiences in (a) teaching literacy practices to their colleagues and (b) how they learned and enacted these practices in their classrooms. Nested in calls by the Common Core State Standards for English-Language Arts (CCSS-ELA) and Response to Intervention (RTI) process, this research is a flagship for literacy integration professional development in mathematics. The MTFs' detailed descriptions provide valuable information regarding the discipline-specific literacy practices of secondary mathematics and offer important considerations for staff developers, curriculum coordinators, including the author, literacy/instructional coaches, and administrators seeking to improve literacy integration. [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.]