This study examined siblings' teaching strategies in 72 dyads (firstborn and second born, M ages = 81.64 and 56.31 months) as a function of dyad age, age gap between siblings, and teacher birth order. One child per dyad was randomly assigned to teach her or his sibling to construct a tractor toy. Interactions were coded for the topic of teachers' speech, specificity of instructions, learner involvement, and how learner errors were corrected. Teachers from chronologically older dyads used more learner-centered strategies, as did those who were second born (age controlled). However, these main effects were qualified by various interactions between age and birth order, generally suggesting that firstborn children's teaching may benefit more from the experience that comes with age. Correlations between strategies also suggested that independent of age, siblings differ in the goals and abilities underlying their teaching behavior. Results support the role that siblings play in development and the value of assessing their teaching interactions. (Contains 4 tables and 3 footnotes.)