This study attempted to answer the question: Is a sibling relationship associated with concept learning of a younger child taught by an older child? Each of the 120 First Grade children in the study had an older sibling in Third Grade; equal samples of 30 sibling pairs were drawn from the population of boys with older sisters, boys with older brothers, girls with older sisters, and girls with older brothers. For half of these children, the older sib served as the teacher of his or her younger sib; the remaining half were re-paired so that the older child taught an unrelated First Grade child. The older child was trained in the concept and taught it to the younger child in a 10-minute session. Male learners scored higher on the trapezoid concept attainment test than female learners; learners scored higher when taught by a female sib than when taught by a male sib or by a female nonsib. Girls teaching their sibs used a deductive teaching method more than other groups. Learners with higher concept attainment scores also showed greater awareness of relevant attributes of the concept. Results have implications for the selection of older children for use in school tutoring programs. (Author)