The supervision partnership in middle childhood was proposed by Waters, Kondo-Ikemura, Posada, and Richters as the last phase of parent-child attachment. The present study elaborates this concept by proposing three components of the supervision partnership: "availability and accessibility," "willingness to communicate," and "mutual recognition of the other's rights." Using data from the National Institute of Child Health and Human Development (NICHD) Study of Early Child Care and Youth Development (n = 1,050), we derived indices of the three components and related them to other attachment assessments and to maternal sensitivity. The three components of the supervision partnership were significantly related to one another, to attachment measured in preschool and adolescence, and to maternal sensitivity measured in middle childhood. The findings lend initial support to the proposal that the supervision partnership may more fully capture the secure base concept in late middle childhood than traditional approaches that focus only on availability and accessibility.