Human factors have an important effect on performance of software teams and resulting software products. One of the seldom-studied aspects of human factors is the effect of personality-based team formation on team cohesion and quality of the software product. In this study, we investigate the above effect by conducting an exploratory case study during a term-long undergraduate software engineering course containing a project component with 50 undergraduate students. We grouped the students based on the social-interaction dimension (introversion/ extraversion) of the well-known Myers–Briggs Type Indicator (MBTI) personality assessment model. We then collected the relevant metrics to explore/analyze the two parameters of interest in our study: team cohesion, and project grade as an indicator of project output (i.e. resulting product quality). Our results show that there is some (although weak) relationship between the team formation scheme (based on either introversion or extraversion) with group performance and project grade. The results also show that mixed grouping of personality types has no significant effect on team cohesion but is advantageous in achieving higher project grades especially for people with low GPAs.