There has been few analyses of relationship between verbal coding/mediation skill and task performance in children's left-right orientation discrimination. In this study, verbal coding skill was evaluated from expression of the orientations of pictures presented prior to the task, and verification of verbal mediation was gained from expression of the response labels used in the task. Developmental change of verbal mediation skill was found in preschool years, although the task was easy to resolve even with nonverbal mediation. Utility of nonverbal mediation in a discrimination task and the nature of a transitional level featured by nonverbal mediation in spite of verbal coding skill were discussed.