This paper focuses on functional thinking as an approximation to algebraic thinking in third-year primary-school students. It describes a study with a class group of 24 Spanish pupils displaying functional thinking to solve a contextualised problem, identifying the type of functional relationships distinguished by these students and the ability to generalise observed in some of them. It contains an analysis of the information collected in one questionnaire, which is part of a teaching experiment. The students distinguished two types of functional relationships, correspondence and covariation, predominantly the former. Three students generalised as well.