This study examines the influence of a year-long mathematics professional development program on Kindergarten teachers' beliefs, content knowledge, instructional practices, and their students' achievement. The professional development program is grounded in the theoretical construct of learner-centered professional development and focuses on supporting teachers' integration of standards-based pedagogies aligned with the Common Core State Standards in Mathematics. Data analysis included examining 15 Kindergarten teachers' mathematics content knowledge, their beliefs about mathematics, their enactment of student-centered pedagogies, and student achievement on curriculum-based assessments. Findings indicated that teachers adopted more student-centered pedagogies and embraced more student-centered beliefs about mathematics teaching during their time in the project. Further, Kindergarten teachers also demonstrated gains in their mathematical content knowledge, and those content knowledge gains were linked to gains in student achievement.