This paper looks at the design process of the WamBam; a self-contained electronic hand-drum meant for music therapy sessions with severely intellectually disabled clients. Using co-reflection with four musical therapists and literature research, design guidelines related to this specific user-group and context are formed. This leads to a concept of which the most relevant aspects are discussed, before describing the user studies. Finally, the plan for the redesign is discussed. The WamBam has unique possibilities to deal with the low motor skills and cognitive abilities of severely intellectually disabled users while music therapists benefit from the greater versatility and portability of this design compared to other musical instruments. A prototype was tested with twenty users. Participants proved to be triggered positively by the WamBam, but three limiting usability issues were found. These issues were used as the fundamentals for a second prototype. Music therapists confirm the value of the WamBam for their practice.