To date research into how young people acquire accurate higher-order scientific knowledge, and gain an understanding of abstract and challenging concepts in science, has occupied much of the science education literature across countries and across continents. In previous studies, we identified that biology teaching that involves the diagnosis, reduction and elimination of misconceptions can be one effective pedagogic approach, particularly if positioned within a ‘good enough’ model of pedagogic practice . In this study, we investigate the use of one diagnostic testing approach to the identification of misconceptions in the teaching of respiration and photosynthesis in a small sample of secondary school students (n=139) and pre-service teachers (n=43) in the Republic of Ireland. Photosynthesis and respiration were chosen as they are prevalent biology topics that students find conceptually challenging. The study used test items to elicit the extent of misconceptions among this cohort – a paper-and-pencil test for students and a survey instrument for pre-service teachers. The findings show unacceptably high level of misconceptions among all pre-service teachers and students and suggest that diagnostic tests of this type can be a useful entry point to a pedagogical cycle for the recognition, reduction and removal of misconceptions. The findings have wider implications than this small scale study and are primarily directed toward new understandings in relation to more effective models of biology teaching and teacher education.