Repertory grid analysis was employed as a means of constructing representations of learners conceptions of living things (described in previous work). Experts in biology and secondary school science learners were probed for their representations of living things. Clearly, a theory is at work in the mind of the experts. The question now is: how many of the students share this theory? A record of commonality is required, and for that a social network framework is necessary. Therefore, representations were compared using the SOCIO program which measures the similarity between individuals and a visual network produced for the groups studied. This work is part of an overall project examining the learners’ innate ability to classify and categorize living things. Classification and categorization are neglected in science curricula which has implications with respect to the renewed emphasis in education on learning about biodiversity. It was found that whereas there is a commonality with respect to learners’ conceptions, the commonality is measurable and that learners often operate within a ‘pre-scientific’ or folk-biological mode, experts operate within a highly formalized mode based on their training, and that notwithstanding such a difference in modes, there remains a degree of commonality between learners and experts.