In part one of this fourth in a series of online professional development sessions, “Essential Practices for Wondrous Science,” teachers construct an understanding of the practice of Developing and Using Models. Interactive activities will help participants learn how models are integral to the practice of science and are used across many disciplines in a variety of ways. Helping students develop and test models supports their learning by making thinking visible and helps them understand important aspects of how science and engineering work. Models can also be strategically used as a means of assessment. As participants explore the tenets of modeling across grade bands they will discover how developing and using models can be a powerful tool for understanding.