The teaching of mathematical modeling is limited in P-12 classrooms. Little is known in regards to how to support teachers to successfully enact modeling activities. Teachers do not always appreciate the value of modeling activities in mathematics learning and often feel unprepared to implement modeling in their classrooms. Teachers often struggle with the concept of mathematical modeling and need more clarity pertaining to what constitutes authentic modeling activities. The purpose of this study was to examine how teachers' understandings of modeling (e.g., process, task features) and their attitudes toward teaching mathematical modeling evolved and developed as they carefully: (1) analyzed modeling tasks and made sense of their curricular and pedagogical opportunities; (2) planned and enacted modeling tasks; and (3) reflected on their enactment through the lens of curricular and professional noticing. The participants of this two-phase (curricular noticing followed by professional noticing), multi-tiered (student, teacher, researcher) design research were eight math teachers enrolled in a five-semester secondary (6-12) teacher preparation program at a liberal arts public university located in the Southeastern region of the United States. Research procedures focused on implementing a potentially adaptable and replicable module over a 15-week, semester long student teaching/internship course. The module was designed for teachers to develop skills and competencies for: (a) effectively enacting modeling activities in 6-12 classrooms in mathematically and pedagogically productive ways; and (b) noticing the pedagogical opportunities embedded in the model eliciting activities, as well as the affordances and limitations of the tasks. The results of this dissertation study show promise for using the curricular and professional noticing frameworks to transform and expand teachers' understandings of mathematical modeling. The results also support mathematical modeling as a rich and valuable context for helping teachers develop curricular and professional noticing skills. The analyses provide pedagogical implications for mathematics methods courses and mathematics teacher professional development, and they should be especially useful to professionals in teacher training who have genuine concerns over how P-12 mathematics education may contribute to the development of 21st century skills such as adaptability, systems thinking, nonroutine problem solving, and complex communication skills. [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.]