Which statement is true according to Duvall and Miller's developmental theory of families?

The statement that families demonstrate common forms of membership across developmental stages is accurate according to Duvall and Miller's developmental theory of families. This theory posits that while each family has its unique characteristics, there are identifiable developmental stages that families generally pass through. These stages include events like marriage, childbirth, and launching children into adulthood, where families typically exhibit shared patterns of behavior and responsibilities.

Through these common forms of membership, families navigate changes in dynamics, roles, and functions that occur throughout the family lifecycle. For instance, the transition from a childless couple to parents brings about changes that are predictable and shared by many families, highlighting the importance of shared experiences in family development.

While families may indeed be unique (as indicated in the other choice) and influenced by external environmental factors, these elements do not negate the overarching patterns seen across many families as they progress through similar developmental stages.