Background: Studies of group creativity have focused on adults acting in professional settings, with less attention paid to how adolescents collaborate in groups in creative activities. Building on sociocultural perspectives on imagination as a complex capacity in adolescence, this study examines students' creative-imagining processes and the role of peer influence in group collaboration. Methods: The setting of the study is a two-day museum-led workshop on the topic of architecture, which was produced for a national touring program for middle schools. Video data of students' collaborative interactions comprise the primary data for the analysis. Findings: The study identifies material, institutional and relational aspects of group creativity in adolescence. A key finding is how creative influence is socially negotiated when merit-based knowledge and authority in an art domain are not valued. The study also finds that students' interactions in creative activity may be viewed as evidence of learning processes even without consensus in the group. Contributions: This research contributes new understandings of adolescents' creative-imagining processes and creative influence in arts-based learning activities in middle school. Principles for arts-based learning designs are presented: the appropriateness of materials; designing for knowledge dependency in open-ended tasks; and facilitating productive forms of creative influence.