Final answer:
Developmental psychologists make common assumptions about development in terms of the lifelong process across different domains, the nature of development (continuous or discontinuous), the existence of one or multiple course(s) of development, and the influence of nature versus nurture on development.
Step-by-step explanation:
Developmental psychologists make several common assumptions about development. Firstly, they view development as a lifelong process that occurs across three domains: physical, cognitive, and psychosocial. They also consider whether development is continuous or discontinuous, whether there is one common course of development or many unique courses, and the relative influence of nature versus nurture on development. Lastly, they examine normative development by determining average ages at which specific developmental milestones are reached.