The main goal of the present study was to provide insights into how disciplinary expertise might be infused into Design and Technology classrooms and how authentic processes based on professional design practices might be constructed. We describe elementary students' collaborative lamp designing process, where the leadership was provided by a professional designer. The video-recorded lessons on lamp designing and the "Lamp Designing" view of the project's database constituted the data sources of the study. A data-driven qualitative content analysis was conducted for categorizing the scaffolding activities of the designer. The results indicate that the designer's participation opened up the world of designing for the students. This enabled the students to engage in embodied design practices, and to gain new insights of the professional mechanisms of designing. Having the professional designer working with them, provided students with the opportunity to gain the full potential that solving complex design problems can offer to learning.