A key role in the development and deployment of Assistive Technology solutions is that of the "assessor-consultant". Assessor-consultants for the UK-based charity Abilitynet work with clients to develop customized computer-based assistive technology systems and draw on a range of shared knowledge from the assessor-consultant community. We provide examples of the process by which assessor-consultants develop systems for clients with complex difficulties and progressive conditions such as motor neurone disease. We draw attention to the fact that evaluation studies of interventions consist largely of generic findings that are difficult to apply in assessor-consultants' everyday work with clients. Analysis of case histories and interviews with experienced assessor-consultants suggests that reconstructing their work as a knowledge construction activity could form the basis of a shared and collaborative culture of practitioner research. We draw on recent work on knowledge construction and innovation to suggest possible means by which this might be supported.