This paper examines how social sources influence individuals' thinking, acting and construction of knowledge. Reconciling both cognitive and sociocultural constructivist perspectives, it proposes that the particular situations in which individuals engage in vocational activities should be included in frameworks which seek to explain the social genesis of knowledge and its construction by individuals. Engagement in these activities is held to lead to the transformation of individuals' knowledge through an active and reciprocal process of knowledge construction and reinforcement. This engagement, furnishes access to knowledge which is shaped by social sources comprising situational factors and socio-cultural and historical levels of development. Learning is viewed as the outcome of participation in activities within particular situations. Individuals' existing knowledge interacts with that sourced in history, culture and community during engagement in goal-directed activity. Therefore, views about relationships among social sources, thinking and learning need extending to incorporate more fully the roles that particular social circumstances play in the construction of individuals' knowledge. Consequently, the Vygotskian levels of development need to be augmented by the inclusion of the unique complexes of situational factors of communities of practice where individuals engage in goal-directed activities. However, despite this it is claimed that cognition is not situated, rather being the product of interpretative engagement with social sources which are manifested in particular situations. This view has consequences for the planning of curriculum for vocational education associated with views about curriculum goals, instruction and approach to assessment.