This study investigates how shared picture book storytelling within a peer-group setting could stimulate causal reasoning in children aged 4½ to 6 years. Twenty-eight children from preschool classes of three schools were allocated to one of six groups (four to five children per group). Each group participated in six storytelling sessions over a period of 2 weeks. During these sessions, the children freely generated stories from stimuli in two picture books. Storytelling discourse was analyzed in the groups that showed the lowest and the highest pre- to postintervention improvement on a series of causal reasoning tasks. In the most-improving group, discourse was distinguished by detailed interpretations of perceptual features, causal explanations, and explicit justifications of statements. The least-improving group was distinguished by "superficial" talk (i.e., labeling perceptual features, simple inferences, uncritical acceptance of statements, and disagreements). These types of discourse could be related to time spent on storytelling. The findings generate hypotheses for future research on stimulating causal reasoning in early childhood education.