The social aspects of activity provide for role assignments, problem-solving approaches, interpretations of events, and the ways that events are valued or despised. Because the pattern of activity has such profound consequences for the creation of mind, in sociocultural theory the basic unit of analysis is the activity setting. The activity settings of classrooms need to be created so that when assistance is needed, it is present in each activity setting designed for learning. The chapter examines how social relationships are formed and changed. Shared psychological transformations of understanding and valuing result in intersubjectivity; those in turn produce the transformations of affinity that produce ramifying consequences in social relationships. So, the condition of intersubjectivity establishes affinity. Although affinities are a powerful and predictable force in the classroom, they are often invisible to the participants themselves, be they teachers or students. Intersubjectivity, and its contents, are vital elements of an effective school, and profoundly important for effective teaching and learning.