Formative evaluation plays an important role in the domain of interaction design (IXD). It occurs throughout the design and development processes, with the results of evaluation feeding back to revise the design. How important is formative evaluation in a product design process? Will this method obstruct creativity, or it can inspire and promote better design? In the fall of 2010, students from a senior-level product design course and a graduate-level interaction design course were grouped together to work on a GE Healthcare sponsored design project: home-based health monitors for individuals with Cerebral Palsy, Parkinson’s Disease, Multiple Sclerosis, and Arthritis. Product design students led the overall process of design: investigating the diseases, brainstorming the concepts and finalizing the design with stages of prototypes and computer models. IXD students acted in two roles: designing the interactive design components of the concepts and running formative evaluations iteratively to improve the outcome during the process. They adopted several evaluation methods, including usability testing, interface criticism, cognitive walkthrough, and heuristic evaluation at different stages to evaluate and improve the design outcomes. Instead of being an outside critic, they actively participated in the creation process. Product design students gained from the experience of working in a multi-role team, listening to the evaluation results, and integrating suggestions into their work. This paper reports the structure and outcomes of these design collaborations, highlights the gains and losses in the process, and most importantly, illustrates a potential path to conduct such design education in the future.