Contemporary research from a psychology of mathematics education perspective has turned increasing attention to the structural development of mathematics as an explanation for the wide differences in mathematical competence shown upon school entry and in the early school years. Patterning, multiplicative reasoning and spatial structuring are three areas central to this research. A suite of studies with 4- to 9-year-olds indicates that an awareness of mathematical pattern and structure is crucial to the development of mathematical concepts, skills and proficiencies. This underlying awareness generalises across mathematical concepts, can be reliably measured and is correlated with general mathematical competency. Evidence of young students' difficulties in acquiring structural awareness is described in order to make as explicit as possible the bases for identification of developmental features of mathematical structure. Some implications for instructional practice for students with mathematics learning difficulties are discussed.