Within the framework of our research on learners' language practices and representations, this contribution explores how their representations about language uses and language learning shape the processes of learning and communication in school settings. More precisely, we will study learners' representations regarding the existence of a "plurilingual asset", defined as plurilinguals' strategic advantage for further language learning and use. Following a discussion of the arguments that support the hypothesis of plurilingualism as a potential facilitator for both learning and verbal interaction, we will address the question of the sociolinguistic conditions that must be met for learners to perceive their plurilingualism as an asset in formal education. Special attention will be paid to the impact of a third language learnt at school on the construction of plurilingual repertoires and on the evolution of learners' representations about languages, language uses and learning as their repertoires widen and diversify. The population under study includes young plurilingual learners in two secondary schools and one university in France and Germany. The analysis of their discourse and underlying representations about the role of prior language knowledge in language behaviour and learning experience will allow us to discuss the role played by the institution in encouraging learners to view their plurilingualism as a strategic resource. (Contains 6 notes and 2 figures.)