Developing staff competence in evidence-based interventions for people with a severe mental illnesses is now a government priority. However, evidence concerning the nature and effectiveness of the training programmes that are designed to develop competence is decidedly limited. The purpose of the present study was, therefore, to evaluate systematically a manualized and evidence-based staff training programme. This programme was delivered over a 17-day period, in a modular and experiential workshop format. Staff (mostly mental health nurses) were allocated to either an experimental group (N = 18) who received the training or to a waiting-list, control group condition (N = 7). Multi-dimensional process and outcome evaluations indicated that the staff training was delivered competently, followed an experiential learning approach, and led to significant improvement in the participants' targeted knowledge and skills. The staff were also satisfied with the acceptability and delivery of the training. Generalization to the participants' clients was reported to be very good, which was congruent with evidence of a supportive work environment, the organizational evaluation aspect of this study. While these learning outcomes are typical of such training, the degree of generalization is exceptional. Possible reasons for this favourable outcome are discussed, and conclusions are drawn for developing staff competence in ways that maximize the delivery of evidence-based practice.