The study of preservice elementary teachers' knowledge of fractions is important because fractions are notoriously difficult to learn and teach. Unfortunately, studies of preservice teachers' fraction knowledge are limited and have focused primarily on division. The present study included all four operations to provide a more comprehensive understanding of this knowledge. Because knowledge is complex, it was examined in five ways: computational skill, basic concepts, word problems, flexibility, and transfer. To further capture the complexity of knowledge, solution methods were examined for patterns that might reveal understandings and misconceptions. Data were gathered before and after a course designed to deepen preservice teachers' knowledge. Quantitative and qualitative shifts occurred during the semester, but flexibility and transfer were low. Implications for teacher education are discussed. (Contains 6 tables, 1 figure, and 1 note.)