This chapter presents the current view of the nature of children’s thinking. During the last few decades, research on learning combined with the wisdom of practitioners have given us important new ideas to consider about deepening students’ understanding of scientific principles. This chapter looks at these ideas, the past and current research behind them, and implications for the classroom when teaching for conceptual understanding. Reflection questions are provided at the end of the chapter, as well as suggestions for available NSTA resources. Teacher background information, standards, and assessments are included. This book selection also includes the Table of Contents, Preface, About the Authors, Introduction, References, and Index.