In this paper we propose to apply domain ontologies in agile software development to reduce the ambiguity caused by using natural language as ubiquitous language to report user stories. To justify and demonstrate our approach, we present a case study that combines Scrum and Behaviour-Driven Development (BDD) in the development of an educational support system, which was built to support the activities of the Medicine Programme of Federal University of São Carlos (UFSCar) in Brazil. Starting from a reference ontology for the Higher Education domain, we gradually specialized this ontology for this programme. Since we selected the Evaluation Management module of this system for our case study, we applied the Evaluation Process Ontology to that programme, and defined user stories to identify the feature set to be implemented. For evaluation and validation purposes, we assessed the quality of all ontologies used in this work according to structural and functional dimensions.