Competencies may be defined as the knowledge, skills, and professional dispositions that an individual is required to demonstrate in order to be considered professionally competent. Competency-based education has long been a feature professional degree programs, but the discipline of Computing Science has only recently begun to embrace competencies as a means of structuring or evaluating students’ learning. Meanwhile, the practice of work-based learning - also well-established in other professional disciplines - has become more prevalent in Computing Science education, with increasing emphasis placed on work-based modes of learning, such as internships and apprenticeships. In this paper, we examine how students enrolled on a degree-level apprenticeship in Software Engineering have developed their professional competencies in the workplace. The paper is based on an analysis of 38 student assignments, wherein apprentices were asked to identify the competencies they have demonstrated, with reference to a portfolio of work. The UK Standard for Professional Engineering Competence and Commitment, which outlines the competencies required for certification as an Incorporated Engineer, provided the necessary framework. Competencies relating to ‘communication and inter-personal skills’ were among those most often cited by apprentices, with competencies relating to ‘knowledge and understanding’ and ‘design and development of systems’ also featuring prominently. Competencies relating to ‘responsibility, management, or leadership’ were less prevalent, with ‘professional commitment’ proving to be the least commonly cited category of competencies. We provide examples of how apprentices claim to have demonstrated each competency, and discuss the implications of these findings for competency-based learning in Computing Science education.