Case analysis is often used in early childhood teacher education as a constructivist method for developing students' professional skills and knowledge. Although case-based instruction is popular, the professional literature contains little empirical evidence that it effectively helps students develop professional knowledge. Indeed, some empirical evidence suggests case-based instruction may negatively impact learning, especially for students with limited existing knowledge about children's development. This study compared the child development content knowledge gains of two classes of undergraduate preservice early childhood teachers: those taught child development with case-based instruction and those taught the same content with traditional didactic instruction. The study also sought to determine if students' level of prior knowledge interacted with the type of instruction they received. Results indicated that students with strong prior knowledge out-performed classmates regardless of instructional method (i.e., case-based or didactic instruction). Students at all levels of prior knowledge had similar knowledge gains across both case-based and didactic instruction, but data trends suggest students with the least prior knowledge gained the most knowledge with case-based instruction. (Contains 7 tables.)