A case study detailed the influence of a nine-year-old female sibling on the writing development of her younger brother, from the time he was 18 months old until he was 28 months old. General and significant interactions, such as the boy's oral language milestones and the books the children shared, were recorded in a journal by their mother. Periodic transcriptions of reading and writing interaction were also made, and writing samples from both children were collected. Results indicated that although the older sister exhibited several teaching techniques--such as providing writing examples, demonstrating functional contexts for writing, organizing materials and writing sessions, and acting as researcher--her immaturity affected her teaching ability. Her choices of reading materials to share with her brother were not always appropriate, and at times, the children fought violently, despite the eight-year age difference. Findings suggest that parents should be concerned with teaching older siblings how to encourage literacy in younger siblings and how to supervise sibling interactions. (NKA)