The teacher-pupil relationship represents an important dyadic model, which focuses on information exchange and holds that the fundamental process through which information is disseminated is a dyadic one, defined as two people: a teacher and a learner. The teacher-pupil dyad model suffers from some of the same problems as are found in the mother-child dyad model. The focus on dyadic interactions enables the investigator to easily explore the direct consequences of the action of one member on the behavior of another. The history of the measurement of dyadic interactions should immediately alert one to the major problems they face when they measure the more complete effect of the social environment on the child. Investigations of the effects of birth order on caregiver-infant interaction have also considered extradyadic influences. The need to go beyond the dyad is clear if one can understand the infant and child's social and emotional development.