Exploring the applicability of achievement goal theory in participatory design, we present a case study where ten students from two primary schools in Namibia and Finland jointly co-designed an online educational game. The aim of the case study was to identify participating students’ achievement goals, as well as exploring their perceived goal approximations, achievement emotions, and engagement throughout the three-month co-design study. Furthermore, we explored the reflection of achievement goals within the co-designed product. Participants’ achievement goals were identified with an open-ended written task and a q-sort task at the beginning of the study. Throughout the study, students self-reported on their emotions and engagement, as well as on the extent to which the co-design sessions aligned with achievement goals. At the end of the study interviews were held with the students and their teachers. Based on new insights emerging from our findings and reflections, we delineate suggestions concerning the utilization of achievement goal theory within participatory design projects.