This text studies the operation of the system of on-the-job training at constructions sites in Brazil. It shows that the absence of an organised apprenticeship structure, despite a considerable need for qualified workers, is only apparently paradoxical, and, in fact, can be explained by examining the concrete interests of the actors involved. Supervisors on the site control training and promotion, and they use it as a tool to manage and put pressure on the workforce and generate their loyalty. This situation causes resentment among the workers, especially the unskilled who complain that their competencies are not recognised and their bosses are miserly about offering technical advice and promotion opportunities.