The present study aimed to investigate pre-service teachers’ mathematics teaching when responding to virtual pupils’ unexpected mathematical questions concerning how to sort fractions. The research was conducted with 102 pre-service teachers participating in a teacher education program specializing in upper elementary school mathematics. The main data collection strategy took the form of video recordings of teaching sessions involving semi-virtual simulations. The recordings were analyzed through a qualitative explorative analysis process involving three phases, focusing on the object of learning and how the pre-service teachers handled the mathematics content pertaining to comparing fractions. The simulated teaching activity, together with the large sample, allowed us to discover patterns concerning how PSTs teach when they are asked unexpected questions related to fractions. The results show qualitatively different ways of teaching. PSTs draw pupils’ attention to different learning objects by using different representations and more or less correct mathematics. This study offers teacher educators knowledge about how PSTs teach when confronted by students with unexpected questions concerning fractions and can therefore support teacher educators in interpreting students’ mathematics instruction and help them decide how best to support PSTs’ teaching instruction.