This study offers insights from an initial pilot of a co-teaching model for mathematics teacher preparation developed both to support experienced teachers in shifting their practice toward the vision set forth by NCTM and the Common Core State Standards for Mathematics (National Governors Association, 2010; NCTM, 2000, 2009) and to provide opportunities for preservice teachers of mathematics to gain experience with teaching practices better aligned with the new standards. Co-teaching is emerging as an alternative to the traditional student teaching experience, in which teacher candidates gradually assume full responsibility for instruction, assessment, and management in their field placement settings, a model that has not changed significantly in more than 50 years (Bullough et al., 2003). Based on effective practices in special education (Cook & Friend, 1995), co-teaching involves two teachers sharing the planning, teaching, and assessment of groups of students in the same physical space. In the context of special education, the two teachers are a general educator and special educator. Much has been written about these co-teaching partnerships and the benefits for students with special needs who are served in general education classrooms, and it is not uncommon to see a special educator working alongside a general educator in elementary and secondary classrooms, including mathematics classrooms. In the context of teacher preparation, the co-teachers are a teacher candidate and the cooperating teacher. In this model, the teacher candidate is involved in teaching from the first day in the classroom, and the cooperating teacher maintains a high level of involvement throughout the experience. In this article, the authors report on the use of a co-teaching model developed and implemented specifically in foundational level mathematics courses in high-need schools.