To be able to support meaningful mathematical experiences, preservice elementary school teachers (PSTs) must learn mathematics in deep and meaningful ways (Ma 1999). They need to experience investigating and making sense of the mathematics they will be called on to teach. To expand their own--often limited--views of what it means to teach and learn elementary school mathematics, they also must observe and experience elementary school children investigating and making sense of important mathematical ideas. Filled with memories and past experiences, PSTs are inclined to teach the way they were taught (Ball 1990); therefore, teacher educators must take every opportunity to transform, nurture, and support PSTs' beliefs about mathematics teaching and learning. This article describes how Kelly McCormick uses videos of children exploring fundamental mathematical concepts as a means to help motivate her students to develop a deeper understanding of the mathematics that they are called on to teach. Moreover, the videos and the act of experiencing the same rich tasks and parallel discussions challenge and shape PSTs' beliefs about mathematics teaching and learning by situating their learning within contexts that occur in real elementary school classrooms (Lannin and Chval 2013). Specifically, the article discusses how McCormick launches a PST content course using a video entitled "Sharing Submarine Sandwiches, Grades 5-8: A Context for Fractions" (Dolk and Fosnot 2006), in which fourth and fifth graders explore fundamental fraction concepts.