This book is a result of a major research project in Switzerland that brings together the fields of Education and Socio-Cultural Psychology. It is focused on how culture is involved in very concrete educational practices. The reader is invited to follow the research group in a Swiss technical college that trains young people in precision mechanics during a period of major technological change: the arrival of automated manufacturing systems. This transition in the trade is an opportunity to explore the educational and psychological challenges of vocational training from a perspective inspired by activity theory and the consideration of social interactions and semiotic or other technical mediations as crucial to the formation of professional identities and competencies. What are the most appropriate settings for learning? There is no simple answer to this question. What can lead a pupil to become engaged, even if this is within a school, with all the seriousness of a future professional? Under which conditions is an internship in a company genuinely formative? Is it necessary to possess the most recent technologies in order to offer high quality training? What do we know about the relation between doing and knowing in the construction of new competences? How can it be planned and informed to become an object of reflection and make sense in the eyes of the learner? Dealing with such qustions, this study explores new working hypotheses on the manner in which the young experience their training and on the significant role for them of professional specialization.