Mobile apps can be used for productivity, entertainment and communication, but did you know they can also be used for science? In this talk we will explain how we developed a mobile app to aid research on anxiety treatment. Children with specific fobia, like fear of spiders or dogs, can mitigate these fears by practising. The purpose of this app is to coach the children during this practise. We will discuss how the various scientific principles were implemented in the application and how we used feedback from child panels to optimise the design of the app. We will show which mechanisms we impl