Taking as its motto the picture book Zoom, a classic by Hungarian Istvan Banyai originally published for the children's segment, the article discusses reading mediation in libraries based on dialectics, grounded mainly in historical materialism and historical-critical pedagogy. It constructs and presents the idea of reading mediation as a training process that must be committed to the participation of subjects in the written culture, the creation of conditions for the production of mediated knowledge, and, in broader terms, the ontological realization of subjects. It highlights the idea of dialectical mediation as a way to reflect on the mediating practice itself, in its singular, particular and universal dimensions, and as an alternative theoretical and practical approach to reader training that dialogues with understandings of mediation committed to human disalienation, formation, and emancipation