This qualitative study analyses how effective an activity based on the critical and reflexive reading of the historical case of Rosalind Franklin and the elucidation of the molecular structure of DNA can be for learning about the nature of science (NOS). The aspects of NOS addressed are the plurality of methods in scientific research, research objectives, the strengths of scientific models and the epistemic and non-epistemic obstacles faced by scientists in the course of their research. The activity was implemented during a science teaching course for pre-service elementary teachers (PETs). The data were extracted from the PETs' reports, analysing them with a rubric based on inter-rater agreement. The results showed the PETs to have overall improved their understanding of the different NOS aspects addressed, and that they gave more importance to non-epistemic than to epistemic factors. In short, the results showed this type of activity to be educationally effective in learning about NOS using cases from the history of science. They also lent support to the view that teaching NOS should take an equilibrated approach to both its epistemic and non-epistemic aspects.