Autistic children find pretend play difficult. Previous work suggests Augmented Reality (AR) has potential in eliciting pretend play in children with autism. This paper presents the evaluation of an Augmented Reality app to help autistic children engage in solitary pretend play. We followed a user-centred design process, involving various techniques and stakeholders. Results from a pre-post study design suggest the AR system is promising in facilitating quantitative aspects of pretend play in autistic children.