Background:The early algebra curricular proposal seeks to promote algebraic thinking from the first educational levels. Functional thinking is an approach intended to promote algebraic thinking in students. At present, various curricular programs include notions related to this thinking. However, this type of thinking has had little influence on prospective teachers, thus arising the need to investigate how they approach tasks to prepare them adequately for their teaching. Objective: To analyse the strategies that prospective Chilean primary education teachers use when they solve a task that implies the generalisation of a functional relationship. Design: We follow a qualitative methodology at an exploratory-descriptive level. Setting and participants: The sample included 18 prospective primary education teachers from a Chilean university. Data collection and analysis: We collected the data through a written test in a group of 18 prospective teachers who were in the first year of training and analysed the data. Results: We highlight the diversity of arithmetic and functional strategies used by prospective teachers. In addition, we highlight their trajectories to solve the task, finding that most of them begin using arithmetic strategies and end using functional strategies. Conclusions: This research will identify the strategies used by prospective primary education teachers and whose data could be useful for the creation of teacher education programs.