Whilst attendance at short, day-long courses or workshops features prominently in teachers' continuing professional development (CPD) profiles, research remains equivocal about their lasting impact. The present study addresses questions about the impact of short-course CPD in the context of a national CPD programme aimed at developing teachers' and teaching assistants' self-efficacy in relation to inclusive physical education. A repeated measures design was adopted to examine the contribution of the CPD programme to participants' self-efficacy. Data were collected from n = 1533, n = 1432, and n = 149 teachers and teaching assistants at baseline, immediately after the course, and 3-6 months later as a follow up. Results suggest that short-course CPD can positively affect teachers' and teaching assistants' self-efficacy in the short term. However, longer-term benefits were confounded by gender, age, years experience working in the profession, efficacy beliefs prior to attending the CPD course, and perceptions on the quality of the course attended. The results of this study reinforce existing research that the effectiveness of short-course CPD is dependent on a range of individual factors and perceptions on CPD quality, and that greater tailoring of delivery is required to ensure that learning is maximised for all involved.