The goal of this study is two-fold: 1) to examine the role content knowledge plays in prospective teachers’ (PSTs) ability to recognize children’s conceptual understanding of mathematics, and, 2) to examine examined PSTs' ability to recognize evidence of children’s conceptual understanding of mathematics in three content areas before and after an instructional intervention designed to support this ability. The results of this study suggest that content knowledge is necessary but insufficient in supporting PSTs’ ability to recognize evidence of children’s conceptual understanding of mathematics.