In spite of a lack of consensus about the nature of scientific models, the role of models and modeling are well established in the practice of science. Students who participate in developing, validating, deploying, and refining models are engaged in authentic scientific practices. Modeling Instruction developed to promote the role of models and modeling in introductory university physics classes. Modeling Instruction for university physics is founded on the basis of two theoretical foundations, Modeling Theory of Science and Modeling Theory of Instruction. We claim that the translation of these theories into classroom practice supports learning in science. We substantiate this claim by first describing how these theories establish complementary cycles of content development and student participation. Then we provide evidence of these interacting cycles by analyzing the development of a conceptual model in a Modeling Instruction university physics class using video data. The video data we present includes students developing a scientific conceptual model first in a small student group and a later in the full class.We argue that the integration of the theoretical components underlying Modeling Instruction are key supports in providing the opportunity for students to develop conceptual models and engage in the practice of doing physics.