In a recently concluded exhaustive, qualitative investigation carried out in an evening primary school in Mexico City, we follow the case of Lucina along with four others. The research alternated the use of natural numbers, fractions and decimals; here we deal exclusively with the semantic and conceptual enrichment of fractions, in the resolution of problems which allow the reconstruction of vital experiences of the subject. The study was made up of an exploratory questionnaire and two didactical interviews with this 41-year-old woman who attends 6th grade elementary school, the interviews being the main source of information of the study. We have selected Lucina' s case because she has recently returned to school, has shown a solid performance on the questionnaire and a satisfactory level of reflection on the nature of her own development.