Based on the responses of our sample (N = 310) of adolescents and young adults from Slovenia (students of secondary and tertiary schools, university students) to a number of tasks covering reproduction, from the molecular to organismal levels, it can be concluded that their knowledge is seriously flawed. Correlations of knowledge between individual tasks are low, or even negative, showing patchiness and missed connections between different aspects of reproduction. Our study confirms the well-known difficulties in building a consistent body of knowledge on the genetic-inheritance axis while expanding it to the anatomy and physiology of reproduction. It is crucial to stress the quality of elementary school biology, and science (biology) courses in secondary schools because, for most people, this will be the last formal contact with some important topics that could influence their life decisions.