There is a paucity of research on therapist competence development following extensive training in cognitive behavioural therapy (CBT). In addition, metacognitive ability (the knowledge and regulation of one's cognitive processes) has been associated with learning in various domains but its role in learning CBT is unknown. To investigate to what extent psychology and psychotherapy students acquired competence in CBT following extensive training, and the role of metacognition. CBT competence and metacognitive activity were assessed in 73 psychology and psychotherapy students before and after 1.5 years of CBT training, using role-plays with a standardised patient. Using linear mixed modelling, we found large improvements of CBT competence from pre- to post-assessment. At post-assessment, 72% performed above the competence threshold (36 points on the Cognitive Therapy Scale-Revised). Higher competence was correlated with lower accuracy in self-assessment, a measure of metacognitive ability. The more competent therapists tended to under-estimate their performance, while less competent therapists made more accurate self-assessments. Metacognitive activity did not predict CBT competence development. Participant characteristics (e.g. age, clinical experience) did not moderate competence development. Competence improved over time and most students performed over the threshold post-assessment. The more competent therapists tended to under-rate their competence. In contrast to what has been found in other learning domains, metacognitive ability was not associated with competence development in our study. Hence, metacognition and competence may be unrelated in CBT or perhaps other methods are required to measure metacognition.