This qualitative study explored elementary teachers' perceptions about the effective features of explicit-reflective nature of science (NOS) instruction. Our participants were four elementary teachers from a public charter school located in the Southwestern U.S.A. The four elementary teachers participated in an academic year-long professional development about NOS which consisted of NOS training and NOS teaching phases. After each phase of the professional development, we specifically asked our participants which features of the explicit-reflective NOS instruction they found effective in improving their NOS conceptions by presenting pre- and post-profiles of their NOS conceptions. We identified nine features perceived by the participants as effective components of explicit-reflective NOS instruction: (1) specific focus on NOS content, (2) participation in hands-on NOS activities, (3) introductory NOS readings, (4) multiple types/forms of reflection, (5) multiple exposure to NOS content, (6) structural consistency in the presentation of NOS content, (7) the evaluation of secondary NOS data from elementary students, (8) the analysis of national and state science standards in terms of NOS content, and (9) NOS teaching experience.