This study employed a case study design (Yin, "Case study research, design and methods," 2009) to investigate the processes used by 5th graders to design and develop computer games within the context of their environmental science unit, using the theoretical framework of "constructionism." Ten fifth graders designed computer games using "Scratch" software. The results showed students were able to design functional games, following a learning-by-design process of planning, designing, testing, and sharing. Observations revealed that game design led to opportunities for informal knowledge building and sharing among students. This, in turn, encouraged students to test and improve their designs. The findings support the conclusion that elementary students can develop programming concepts and create computer games when using graphical programming software developed for their level of experience. Insights into the iterative process of learning-by-game design are presented. (Contains 2 figures and 2 tables.)