This article explores the microgenetic development of learners' understanding of sociolinguistic variation in French during an instructional conversation (IC) that followed a language analysis task in which learners attempted to formulate hypotheses about the nature of language variation. During the IC, the instructor led students toward a conceptual understanding of variation in French by providing appropriate graduated (i.e. from implicit or strategic to explicit) mediation that was sensitive to the class's zone of proximal development (ZPD). Teacher-student collaborative interaction within a group's ZPD has the potential to develop learners' conceptual understanding of variation, which can provide an important orienting basis for the development of their performance abilities. The transcript of the IC is analysed and discussed with regard to the amount and type(s) of mediation the instructor provides and opportunities for development created in this type of collaborative interaction. (Contains 1 figure, 1 table and 9 notes.)