<p>Diarrhoea is a leading cause of morbidity and mortality among under-five children in India, primarily due to inadequate maternal knowledge on home management. This case study evaluated the effectiveness of a Planned Teaching Programme (PTP) on knowledge regarding diarrhoea management in the mother of an under-five child attending Rishitha Hospital, Hyderabad. A 23-year-old literate, non-working mother of a 2-year-old child with inadequate baseline knowledge participated in the study. Pre-test assessment using a structured knowledge questionnaire (30 items) revealed a score of 11/30 (inadequate knowledge). A 60-minute structured teaching session using the lecture-cum-discussion method with pamphlets in English and Telugu was administered, covering definition, causes, signs and symptoms, dehydration assessment, ORS preparation and use, feeding practices, and prevention strategies. The post-test conducted after 6 days showed a significant improvement with a score of 27/30 (adequate knowledge). Major gains were observed in ORS preparation, recognition of dehydration signs, and preventive practices. The findings demonstrate that a well-structured teaching programme can rapidly enhance maternal knowledge, support home-based management and reduce complications. This case reinforces the need for routine nurse-led health education in paediatric settings to combat diarrhoea-related burden in vulnerable populations.</p>