Naturalistic dyadic sequences of teaching and learning involving older and younger siblings were investigated in 39 middle-class dyads over a 2-year period in early childhood. Siblings were observed during ongoing interactions in the home setting for 6 90-min sessions at both Time 1 (older sibling M age = 4.4 years; younger sibling M age = 2.4 years) and Time 2 (older sibling M age = 6.3 years; younger sibling M age = 4.4 years). Sequences of sibling-directed teaching (T1 n = 353; T2 n = 1,039) were identified from the observation transcripts and coded for teacher/learner roles, initiation of teaching, teaching strategies, and learner response. Older siblings were more likely to engage in teaching at both time points, but the proportion of younger sibling teaching increased significantly from T1 to T2, partially because older siblings requested teaching more often from their younger siblings at T2. Siblings’ use of teaching strategies varied across time points, while both older and younger sibling learners generally accepted or complied with the teaching. A final set of analyses examined birth-order effects while controlling for age by comparing older sibling teachers at age 4 (T1) to younger sibling teachers at age 4 (T2). At T1 firstborn older siblings (age 4) engaged in a wider range and more sophisticated teaching strategies than secondborn younger siblings (age 4) at T2. Findings highlight the bidirectional nature of teacher–learner interactions and are discussed in light of recent theory and research indicating that the sibling relationship is a rich context for children’s learning and development.