This study examines the development of mental models of air by kindergarten students after completing a series of hands-on, inquiry-based science lessons. The lessons focused on two properties of air: (1) that air takes up space and (2) that it is made of particles ("balls of air"). The students were interviewed about their ideas of air and about phenomena involving air before and after the lessons. From the lessons, the students gained experiences and vocabulary to draw upon to make more sophisticated arguments about phenomena involving air, often employing the "balls of air" model in their explanations.