A major issue in introducing new technological tools in the classroom is that the teachers who are meant to use them often do not receive the necessary training. This is the case of electronic dictionaries, which are seldom used by both students and teachers, despite their benefits for improving vocabulary development and academic achievement [14]. We propose to address this issue with STI-DICO, an Intelligent Tutoring System (ITS) to help French teachers-in-training acquire both the linguistic knowledge and the practical skills needed to successfully use electronic dictionaries [7]. ITS are advanced intelligent learning environments aiming at providing learners with adaptive tutoring services, relying on a cognitive diagnostic to adapt to learners’ knowledge states at each step of the learning process, based on a formal modeling of the knowledge domain [11]. In this paper, we describe our design-based approach to STI-DICO, the first iterations of which have resulted in the development of a repository of linguistic and meta-linguistic skills, paired with an ontology of lexical concepts and supported by a series of authentic learning activities, all created with the active participation of experts in the field.