The research on the assessment of collaborative problem solving (ColPS), as one crucial 21st Century Skill, is still in its beginnings. Using Tangible User Interfaces (TUI) for this purpose has only been marginally investigated in technology-based assessment. Our first empirical studies focused on light-weight performance measurements, usability, user experience, and gesture analysis to increase our understanding of how people interact with TUI in an assessment context. In this paper we propose a research agenda for assessing ColPS of individuals using the Microworlds methodology implemented on TUIs. In a first example item, we use so-called Micro- DYN items, which are independent microworld scenarios that rely on structural linear equations as underlying model. As the MicroDYN approach has been thoroughly empirically investigated for the assessment of complex problem solving of individuals, it offers a good basis for a reliable and valid assessment. We describe how this approach was applied to create an assessment item for a collaborative setting. This item described in this paper implements a simplified model of a MicroDYN item related to climate change using knowledge of previous studies. Therefore, the focus of the item's construction lies on meeting the requirements for a standardised high quality assessment. Finally, a research agenda is proposed to sketch the main research issues.