The literature highlights the importance of engineering design processes for bringing students in interdisciplinary knowledge and skills. Considering the potential of designing Rube Goldberg Machines in STEM education, this study aims to portray the experiences of fourth grade students designing Rube Goldberg machines in an after-school program for six weeks. A single case study design that approaches an analysis unit holistically was employed. The participants of the study are four fourth grade students (a design team with three female and one male students). The data collection tools were semi-structured interviews and participant observation. The analysis of the data were done via content analysis by creating categories and then themes. The themes that emerged based on the data analysis were design process, use of disciplinary knowledge, use of skills, difficulties faced, problem solving, teamwork cooperation and communication, the comparison between project design and classroom practices, learning, and the role of educator. The findings of the study illustrated the design process and the knowledge and skills they obtained from their own perspectives.