The tradition of storytelling is a distinctive human experience. There have been increasing evidences from social sciences that storytelling facilitates skill development in children. In this paper, we explore the use of humanoid robots to augment traditional storytelling, an area still understudied, to investigate the effectiveness of human-robot collaboration (HRC) in storytelling. In this preliminary experiment, a humanoid robot, Aldebaran's Nao, was programmed to recite a mystery story to 60 students aged 14 to 15, while engaging them through gestures, simulated eye contacts and varied voices. Nao delivered the performance as either an independent storyteller, or as a collaborator with a human storyteller. We assessed the effectiveness of HRC by comparing the participants' preference over the two settings. We found that 1) most participants believe that HRC is effective and prefer HRC over the robot-only performance; and 2) the complementarily effective roles of human and robot storytellers in interacting with the participants provide a glimpse of evidence on the preference towards HRC. These results, provide a first step towards effective use of robots for collaborative storytelling in day-to-day situations, which is well placed to guide the design of robots for education and entertainment purposes, e.g. for improving family bonding between parents and children while allowing parents to more effectively tell stories.