Introduction
Formative and summative assessment each offer distinct benefits for student motivation and learning. In Team-Based Learning (TBL), readiness assurance tests (RATs) can be implemented in either mode, yet their relative impact remains unclear. This study investigates how assessment mode influences preparation, performance, and student experience within a controlled TBL environment.


Methods
A mixed methods design was used across two MSc cohorts (n=64; n=61). Students in each cohort simultaneously took two TBL-based units: one using summative RATs, the other formative. Quantitative data included iRAT/tRAT scores, learning uplift, and (year 2) pre learning engagement. Two-way ANOVA tested effects of assessment mode and team composition. Fourteen students participated in semi-structured focus groups, analysed via hybrid deductive–inductive thematic analysis.


Results
Summative RATs produced significantly higher iRAT and tRAT scores, though uplift was lower. Engagement with pre learning did not differ statistically between units. Focus groups showed summative assessments increased preparation intensity and feelings of accountability but also heightened stress and reduced willingness to take risks. Formative RATs encouraged experimentation, deeper discussion, and greater psychological safety. Permanent teams outperformed rotating teams and were strongly preferred.


Conclusions
Summative RATs increase preparation and grades, while formative RATs foster richer dialogue, risk-taking, and collaborative learning. Stable teams consistently enhance performance. A hybrid model - summative iRAT followed by formative tRAT – is one possibility for future study.