Social-constructivist models of learning highlight that cognitive development is embedded within the context of social relationships characterized by closeness and intimacy (Vygotsky, 1978 Vygotsky, L. S. (1978). Mind and society: The development of higher mental processes. Cambridge, MA: Harvard University Press. [Google Scholar]). Therefore, in contrast to prior research employing semistructured paradigms, naturalistic sibling-directed teaching was examined during ongoing interactions at home. Thirty-nine middle-class, two-parent families (older sibling, Mage = 6;3; younger sibling, Mage = 4;4) were studied. Intentional sequences of sibling-directed teaching were coded for: a) frequency; b) type of knowledge taught (i.e., conceptual or procedural); c) initiation of teaching by the teacher or following a request by the learner; d) teaching strategies (e.g., direct instruction, demonstration); and e) learner responses (e.g., active involvement, rejection). Findings indicated that teachers were most likely to initiate teaching spontaneously rather than respond to direct requests by learners. Teachers were most likely to initiate teaching of procedural knowledge, while learners were most likely to request the teaching of conceptual knowledge. The type of teaching strategy employed depended on who initiated the teaching and the type of knowledge taught. The response of the learner was associated with who initiated the teaching and the teaching strategies employed. These findings reveal the nuances and sophistication of young children's attempts to teach one another naturally in their homes. Findings are discussed in light of recent empirical and theoretical work.