Virtual museums can engage people who cannot visit the museum in person in an immersive experience of the museum collection. The museum diverse displays can help people understand and appreciate cultural heritage while improving their overall knowledge, skills and attitudes. Virtual museum tours have become of great importance to schools -especially when the museums are not in close proximity. This paper describes and evaluates the VISITOR virtual museum app, which enables teachers to select artefacts from diverse collections and add them to their own themed museum. VISITOR combines real artefacts and a constructed virtual space and provides end-users with a 'user as creator' mode.Comprehensive evaluation of such virtual museum tours is, however, needed to ensure their usability and learning potential in the school classroom. We employed qualitative usability testing, and a heuristic evaluation scale based on the literature and the VISITOR's particular aspects. The evaluation results showed that users find the application overall usable, but there appears to still be room for improvement in interactivity and learning potential. Our critical recommendations can inform the redesign of the VISITOR application, and also serve as references for consideration by exhibition or educational technology designers in the design and planning of online virtual museum tours and other virtual tour apps for schools.