This article presents a study of small-group interaction in the context of collaborative learning in undergraduate education. The student groups participated in collaborative projects, which involved setting-up, conducting, and reporting on empirical research studies. This study sheds light on the nature of productive interactions, the joint efforts to co-construct knowledge and the shared epistemic agency expected to emerge when groups are addressing ill-structured, complex problems in a collaboration over time. In-depth qualitative analysis and descriptive statistics were used to analyze and interpret interaction data and developing knowledge objects (i.e., research reports) collected during a 20-week project period. The findings show that productive interactions can take different forms, with discourse-based and object-oriented being the most relevant patterns arising. In the latter case, the emergent knowledge objects also influence the course and productivity of the interaction. Finally, groups manifesting shared epistemic agency produce knowledge objects more complex and suitable to the problems addressed. These findings contribute to a better understanding of the collaborative learning process that includes work on knowledge objects over time. The implications for the educational practice and further research point towards the need for a better understanding of the way groups function when challenged to address complex problems and to participate in knowledge production, how these processes can benefit learning, and what is needed in terms of pedagogical and technological support, to enable students to be more than mere coursetakers, but also producers of knowledge.Keywords Knowledge co-construction . Knowledge objects . Learning in higher education . Productive interaction . Shared epistemic agency . Small-group collaboration In the context of emerging changes in the knowledge-based society, students in higher education are expected to be able to address ill-structured and open-ended problems, conceive new ideas, show inquiring attitudes and proactive behavior, and capitalize on collective expertise (Goodyear and Zenios 2007). Learning in small groups that focuses on solving open-ended problems and on managing the collaborative process has been proposed as a wayIntern.