This study explored third-grade elementary students' conceptions of nature of science (NOS) over the course of an entire school year as they participated in explicit-reflective science instruction. The Views of NOS-D (VNOS-D) was administered pre instruction, during mid-school year, and at the end of the school year to track growth in understanding over time. The Young Children's Views of Science was used to describe how students conversed about NOS among themselves. All science lessons were videotaped, student work collected, and a researcher log was maintained. Data were analyzed by a team of researchers who sorted the students into low-, medium-, and high-achieving levels of NOS understandings based on VNOS-D scores and classwork. Three representative students were selected as case studies to provide an in-depth picture of how instruction worked differentially and how understandings changed for the three levels of students. Three different learning trajectories were developed from the data describing the differences among understandings for the low-, medium-, and high-achieving students. The low-achieving student could discuss NOS ideas, the medium-achieving student discussed and wrote about NOS ideas, the high-achieving student discussed, wrote, and raised questions about NOS ideas.