Designing assessment procedures and interpreting results require a keen understanding of developmentally appropriate expectations for a child within their cultural context. This chapter explains how social ecology shapes maturation and how it is reflected in the assessment process. Four domains of development are presented: Cognitive, thinking and reasoning skills; communication, verbal and nonverbal expressive and receptive language skills, including body language and play; social-emotional, relationship-building and emotional experiencing, recognition, expression, regulation, and response skills; and adaptive, those skills needed to navigate the demands of a person’s environment. We explore how maturation occurs in these domains over four time periods—ages 0–2, 3–5, 6–11, and 12–17 years—and explain how growth varies across social ecologies. Through a series of comparative case studies, this chapter shows how this knowledge informs practice, explaining how assessment procedures need to match the child’s expected development and how interpretation of a child’s presentation must be informed by culturally informed developmental perspectives.