This article describes and analyses a short teaching episode in a multilingual secondary mathematics classroom in South Africa where the teacher is using a participatory- inquiry approach. The episode is used to illuminate the general claim that such an approach, because of the particular communicative demands it places on teachers and learners, can create specific dilemmas of mediation. Teachers are often aware of dilemmas they face. However, what can be obscured is how a participatory-inquiry approach can inadvertently constrain mediation of mathematical activity and access to mathematical knowledge.