The study focuses on examining elementary pupils’ (N = 42, 11–13 years old) reflections on collaborative design processes, team collaboration and their co-inventions. Digital and traditional fabrication technologies were used in a 2-year co-invention project containing approximately 16 sessions during year 1 and 11 sessions in year 2. Between the two project periods, the pupils were asked to write a structured essay about their co-invention and design process, and in year 2 they kept journal notes in each team’s design-folder. Each pupil’s structured essay was analyzed with qualitative content analysis that focused on three main aspects: (1) description of the co-invention, (2) progress of the co-invention process and (3) quality of collaboration. Based on the essay analysis, we constructed a “Co-invention Table” with five categories: user, conceptual design, technical design, appearance, and construction. The nature of the 13 pupil-teams’ co-inventions varied greatly, and these co-inventions were divided according to three main functions: (1) improving cleanliness, (2) providing reminders or (3) addressing well-being. The essays provided information on how creative ideas were generated and how critical thinking and evaluation of ideas were crucial in improving ideas for further development. The collaboration was dependent on everyone’s active and equal participation into work and the importance of an adequate division of the labor was highlighted.