This article describes part of the findings of a teaching experiment whose objective is to investigate the algebraic abilities of elementary students when they solve situations that involve a functional relationship. In particular, we focus on describing the use and meanings attributed to letters by third-year primary school students when faced with verbal problems related to the generalisation of a functional relationship. Drawing from the functional approach to early algebra and set in Spain, the study expands on earlier research conducted on primary school students’ use of letters in algebraic contexts. Their initial reactions to the use of letters to represent indeterminate quantities and how those reactions changed in the course of three sessions are described. Analyses of the students’ written answers together with their participation in group discussions yield qualitative data on how students associate the idea of variability with indeterminate quantities and use letters, numbers or both to represent that notion.

El objetivo de este trabajo es describir una propuesta de enseñanza que promueva el pensamiento algebraico a través de la expresión y justificación de ideas matemáticas al resolver tareas relacionadas con tres enfoques distintos del pensamiento algebraico. Diseñamos un experimento de enseñanza implementado durante la pandemia de la COVID-19 en Chile. Analizamos las discusiones orales y las producciones escritas de niños de cuarto de primaria (9-10 años). Los resultados muestran que los niños expresaron y justificaron ideas algebraicas cada vez más sofisticadas. Es decir, adoptaron paulatinamente un lenguaje matemático más preciso y abstracto. Concluimos que esta modalidad de trabajo, en la cual se destaca el carácter algebraico de la aritmética a través de diversas instancias de discusión, es un aporte para los docentes, al guiarlos en abordar los desafíos de enseñanza actuales.

In this study, we analyze how 9–10-year-old pupils work with equations, a central aspect of algebraic thinking in early grades and a cornerstone for more formal learning of algebra. Specifically, we seek: (a) to describe the main characteristics of the tasks that support algebraic thinking through a translation process from arithmetic word problems to algebraic language and vice versa, and (b) to identify how pupils refer to indeterminate quantities in these contexts and what meaning they give to them. The analysis focuses on the semantic congruence of the expressions proposed by them and on the dialogue they held during the translation process. We analyzed the oral discussion in the pools and the written responses to the problem that pupils posed. The results show that arithmetic word problems allow the indeterminate to become an object of thought for pupils, who represent it in multiple ways and refer to it when proposing equations that represent the structure of each problem. Another finding highlights that reflection on the interpretation of the equations supports the identification of two meanings associated with indeterminate quantities, namely, unknown and variable.