This interpretive case study is framed within recent sociocultural conceptualisations of learning. It draws on research on teacher-led classroom discussions, and investigates the conversational intricacies through which "dialogicity" is accomplished in adaptive ways in one content and language integrated learning (CLIL) science classroom. Multimodal conversation analysis (CA) is performed in order to describe how classroom interactional competence (CIC) is enacted by participants while developing a teacher-led discussion. The data come from a bilingual Catalan-Spanish secondary school classroom in Barcelona in which 16 12-year-old students learn biology in English as a third language. The analysis reveals that: (a) the teacher's systematic deployment of multimodal resources ensures comprehension and favours the emergence of learner-initiated turns; (b) as a result, a highly interwoven set of sequences of "mediation" and "remediation" occurs, jointly providing the students with opportunities for the appropriation of language and content; and (c) this abundance of resources contrasts with the scarcity of teacher moves aimed at eliciting more elaborated learner interventions. The study contributes to further understanding of the relationship between language, interaction and learning. It also shows how multimodal CA may offer valuable tools for tracing the process of integrated learning.