Introduction: From a socioconstructivist and situated perspective of teaching and learning processes, the authors analyze how one teacher and her group of 19 sixth-grade pupils use ICT. The study focuses on the way these tools mediate their activity, and evaluates the tools' potential for teaching and learning innovation. Method: A case study method was used to analyze the development of an instructional unit in natural sciences, where pupils worked in small groups. The sequence was divided into three phases, each comprising different sessions. A model for analyzing educational interaction was applied, based on: a) identification and characterization of the forms of joint activity, and b) a typology of uses of ICT oriented to how the student, the content and the teacher jointly interact. Results: Different uses of ICT are identified as a function of the different phases of the instructional sequence and of the characteristics and challenges presented by the different tasks at each phase. Furthermore, results show that ICTs are primarily used to mediate between pupils and content and, to a lesser extent, between pupils, content, and the teacher. Discussion and Conclusion: In conclusion, the capacity of ICTs to transform educational practice in the classroom depends on the situated use of these tools in authentic teaching and learning situations, and also on new educational possibilities that these tools present for mediating joint teacher-pupil activity. (Contains 3 tables and 2 footnotes.)