First, this chapter will address the significance of observational research within early childhood classrooms, followed by a more specific description of naturalistic observation. Next, a description of existing exemplar measures that tap into the construct of child engagement will be provided, with an emphasis on reliability, validity, and analysis. We will then discuss differences between naturalistic observation of individual children's engagement and global assessments of classroom quality. We end the chapter with an overview of selected findings from studies of child engagement within early childhood classrooms and suggestions for future directions. (author abstract)