This paper considers dynamic assessment (DA) as it relates to second language (L2) development. DA is grounded in Vygotsky's (1987) sociocultural theory of mind, which holds that human consciousness emerges as a result of participation in culturally organized social activities where mediation plays a key role in guiding development. In DA, the evidential basis for diagnosing and promoting development includes independent as well as mediated performance. Unlike in conventional testing, objectivity derives not from standardization, which treats everyone in precisely the same manner; rather, objectivity is argued on the grounds that mediation is guided by a viable theory of mind. Fairness in assessment is thus reframed with the understanding that the quality of support offered may vary across individuals. The paper illustrates how this transpires in the case of classroom-based and formal testing applications of DA with L2 learners. (Contains 5 notes.)