Conducting observational investigations of behaviors and processes is an important method for generating scientific knowledge. This article describes a methodology for assisting students in the processes of observational inquiry and theory articulation and its instantiation in a set of digital video tools. We describe a high school biology curriculum where students use these tools to investigate video clips of animal behavior and develop theories about how and why these behaviors evolved. We focus our discussion on an investigation model that scaffolds students through the processes of observing and explaining video as data and the computational and curricular supports that were designed to make these processes explicit. We conclude with a presentation of preliminary results to illustrate the types of explanations that emerged from working with the software and curriculum and a discussion of issues that emerged during the course of the research.