Young children are exposed to new digital technologies, such as social robots. Limited research exists on how children engage with social robots and their role in the preschool classroom. This study observed 35 English-speaking children (M age = 4.60 years) participating in two tasks (Simon Says and iPad drawing) under the guidance of a social robot or human instructor. Children's engagement was measured across behavioural, emotional, and verbal domains. Results showed higher behavioural and positive emotional engagement with a human instructor than a social robot instructor across both tasks. Children uttered more words with the human instructor than the social robot instructor for the iPad drawing task, although there were no differences for the Simon Says task. Children's engagement and utterances were positively correlated during the social robot and human instructor conditions. The findings suggest that child engagement was overall higher with a human than with a social robot and such differences may be important for teachers to consider when using social robots in the preschool classroom.