This case study analyzes the effect of the Add+VantageMRRTM (AVMR) program on a teacher's pedagogy and on her students' progress in mathematics. AVMR, a professional development program in early mathematics, trains teachers to assess their students' progress and apply those insights to their teaching pedagogy. The AVMR assessment uses a progressive interview approach to determine a student's current level of mathematical proficiency as well as the student's level of sophistication in solving problems. The study centers on an elementary school teacher and three of her students at an Aspen County, New Mexico, elementary school over a nine-month period. For the study, the participating teacher was interviewed and observed over the course of one academic year. Additional data included participating students' Everyday Math Journals, data derived from consultations with the participating teacher's AVMR Mathematics Coach, and participating students' AVMR pre and post-tests. Moreover, qualitative data were obtained through videotaping the teacher's classroom protocol, including how the teacher used AVMR principles and strategies interactively to customize her instruction to meet individual student's needs. The case study results suggest why the three students improved their mathematics skills albeit to differing levels. The results of this study suggest that AVMR mathematical strategies and activities helped to reinforce and build student understanding for the three participating students. The study findings provide evidence that early professional development in mathematics, specifically in AVMR, supported the development of the participating teacher's pedagogy and improved the mathematical achievement of the three participating students. Even though the teacher missed some opportunities, on occasion, to use AVMR techniques, the study strongly suggests using AVMR assessments to reveal what each student knows mathematically, improved the participating students' learning and understanding of mathematical concepts. Furthermore, AVMR benefited the participating teacher by providing a resource that correlates with support areas in the school's mathematics curriculum. [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/en-US/products/dissertations/individuals.shtml.]