There are three aspects of science: (1) scientific knowledge: what we know about the natural world, which would include crosscutting concepts; (2) scientific practices: skills and knowledge necessary for building scientific knowledge; and (3) nature of science (NOS): how science works (Bell et al. 2003). Most science instruction emphasizes the importance of scientific knowledge and practices, but NOS is often left out or not explicitly referenced. However, NOS is critical for understanding how scientists develop scientific knowledge across a variety of disciplines and engage in scientific practices. In understanding NOS, students and teachers have a lens to help them understand the practice of science and its relationship to the world around them. In this article, the authors describe science portfolios implemented in a high school science class so students could reflect on NOS and examine how their conceptions changed and developed over the year.