In Geneva, students completing teacher training in order to become primary or secondary school teachers, produce a portfolio dedicated to professional development. These texts are analysed using linguistic indicators developed by the TALES/TALK research group through a grid named “Analysis of discourses about Professional Apprenticiship” (ADAP). Amongst others, these indicators describe professional knowledge contents, semiolinguistic processes, reflectivity spectrum and regulation systems. Beyond this descriptive level, a hermeneutic analysis brings student’s underlying concerns to light: value systems, motivations and intentions, tensions between scientific knowledge and experience, construction of a professional self. This chapter presents the rationale and theoretical frame that guide this instrument. We then proceed with a detailed description of the indicators and discourse analysis methodology. To conclude, we posit that construction of highly developed professional knowledge depends on a conscious and voluntary process in which the writers transform their subjective preoccupations into objects of reflection and conceptualisation, using the resources of written language as an instrument to think about professional life experienced situations. Finally, the main claim of this study is that discourse analysis enlightens boundaries between reflective writing used to develop relevant valuations about professional situations and to regulate practices; and between concepts and action rules.