Background: Training support staff in dealing with challenging behaviour in clients with intellectual disabilities (ID) is needed. The goal of this study is to determine which elements need to be incorporated in a training on staff interactions with these clients, building upon a framework and an interpersonal model. As in functional analysis, this study tests the influence of client interpersonal behaviour, three types of staff reactions to challenging behaviour, two types of staff psychological resources and staff team climate on four styles of staff interpersonal behaviour. Method: A total of 318 support staff members completed a questionnaire on staff interpersonal behaviour for 44 clients with ID and challenging behaviour, as well as seven questionnaires on client interpersonal behaviour, staff emotions, attributions, self-efficacy, self-reflection, coping styles and team climate. The influence of these seven factors on four staff interpersonal behaviours was examined using multilevel multiple regression analysis. Results: Friendly-warm and dominant client interpersonal behaviour had a significant positive impact on friendly and assertive control staff behaviour, respectively. Also, there was a strong influence of staff negative and positive emotions, as well as their self-efficacy, on most of the staff interpersonal behaviours. Staff self-reflection, insight and avoidance-focused coping style had an impact on some staff interpersonal behaviours. Staff team climate only predicted higher support-seeking staff behaviour. Conclusions: In conducting a functional analysis of staff interpersonal behaviour, the results of this study can be used both as a framework in staff--client interaction training and in clinical practice for treating challenging behaviour. The emphasis in training and practice should not only be on the bidirectional dynamics of control and affiliation between staff and clients, but also--in order of importance--on the impact of staff emotions, self-efficacy, self-reflection and insight, coping style, team climate and attributions on staff interpersonal behaviour.