Associations among sibling teaching strategies, learner behavior, age, age gap, gender, and social-cognitive skills (second-order false-belief and interpretive understanding of knowledge) were investigated in 63 sibling dyads in early and middle childhood. Two teaching tasks were introduced to the older sibling teacher: a teacher-directed task with unique subgoals (tractor construction) and a self-guided, repetitive task (tanagrams). Subsequently, the older sibling taught the younger sibling learner. Findings revealed effects for age and gender; older teachers employed a wider range of strategies, especially in the tractor task, and older learners were more successful and more involved. In the tractor task, teachers also used more instruction and encouragement with same-gendered siblings. Age-gap effects for teaching were evident in both tasks. Further, teachers employed more instruction, help, and demonstration strategies in the tractor task, whereas in the tanagrams task, they engaged in greater encouragement and verbal attention. Learner involvement in the two tasks was positively associated with teaching strategies reflecting guided participation but was negatively related to more controlling teaching strategies. Finally, the two social-cognitive measures were more strongly associated with teaching strategies in the teacher-directed tractor task. Findings are discussed in light of recent theory and research on sibling teaching and learning. (Contains 4 tables.)