Algebraic reasoning is foundational to all mathematical thinking. This is no less the case in the early years of school, where the capacity to recognise the structure of mathematical processes enables students to acquire deep conceptual understanding. It is through algebra, therefore, that students are able to explore and express mathematical structure, pattern and relationships. This article presents using resources from the reSolve: Mathematics by Inquiry Project to demonstrate how, through a structured inquiry process Years 3 and 4 students can investigate the structure of number and generalise the results. This focus on structure sets the foundation for algebraic reasoning.