When a step-sister takes on a teaching role with her step-brother, it can be a unique and valuable experience for both parties. The step-sister can share her knowledge, skills, and experiences with her step-brother, helping him to learn and grow. This can be particularly beneficial if the step-brother is struggling in a particular subject or area. The step-sister can provide one-on-one attention, guidance, and support, which can help to build the step-brother's confidence and motivation.