Research Findings: Sibling teaching and learning behaviors were investigated in 2 studies of children in early and middle childhood. Study 1 addressed individual differences in teaching/learning and associations with dyadic age, age gap, gender, birth order, and relationship quality in 71 middle-class dyads (firstborns M age = 81.54 months; second-borns M age = 56.27 months). Half of the firstborn and half of the second-born siblings were assigned the role of teacher. Regression analyses indicated that dyadic age and age gap made unique contributions to teacher and learner behavior. Few birth order differences in approaches to teaching/learning were revealed. Findings highlight the reciprocal nature of sibling teaching and learning. Study 2 investigated longitudinal associations between sibling relationship quality and teaching in a second sample (at Time 1 firstborns = 46.8 months; second-borns = 14 months). Positive sibling interaction (including play) at Time 1 was associated with teaching/learning behaviors 4 years later. Practice or Policy: Findings are discussed in light of recent social constructivist notions that children's development is facilitated in the context of intimate relationships. (Contains 1 footnote and 5 tables.)