Students' critical thinking is often researched using quantitative tests designed to measure critical thinking. In contrast, this study qualitatively analyses group and whole-class dialogues in an interdisciplinary SSI project by focusing on students' critical thinking practices. As such, the study provides an in-depth example of an immersion approach to teaching critical thinking in an SSI classroom. The SSI project, called the Climate project, lasted 18 lessons and involved an 8th-grade mixed-ability class in a suburb on the west coast of Norway. The data consist of field notes, full-class video recordings and audio recordings of student talk in groups. Based on an interactive ethnographic perspective, patterns in the data were identified using open coding informed by conceptualizations of critical thinking followed by identification and holistic analysis of episodes characteristic of the critical thinking practices in the classroom. The study offers insight into the characteristics of young students' critical thinking in dialogic settings. The students' interpretations, analyses, evaluations, and inferences are based on a mix of knowledge and guesswork. The analysis reveals that the two teachers involved challenged students to, for example, interpret and evaluate information, make inferences, and to suggest alternative views. Explicit teaching of critical thinking was limited. The study demonstrates that it is possible, by employing appropriate teaching strategies, to support students across all levels of abilities in actively participating in critical thinking. Additionally, it shows how specific student centered teaching strategies and students' responses to these strategies contribute to a classroom culture permeated with critical thinking practices.