The relationship between the different mediational means for supporting students' learning with digital tools in science group work in a Norwegian lower-secondary school is examined. Analyses of teacher-student and student-student interactions are located in cultural-historical theory and draw on Galperin's conceptualisation of learning processes. Findings show that digital tools, task design, peer collaboration, and teacher's interventions dialectically interplay to shape how learners use mediational means: (1) digital tools are the resources that enable students to explicate their (mis)understandings; (2) compare-and-contrast tasks promote analytical thinking; (3) peers present themselves as resources who promote development of conceptual understanding; (4) the teacher guides learners' attention towards the potential of the mediational resources, elicits, organises, and structures students' knowledge. The dialectical interplay of these mediational means creates a system that supports and guides students' learning.