Elementary school mathematics instruction aims to develop children's understanding of both numerical and spatial mathematics--two key areas of mathematical learning. The present study explored how learning within one of these areas may impact the other. Specifically, it investigated whether a measurement-to-number intervention designed to increase children's understanding of measurement would also affect the growth of symbolic numerical knowledge. The intervention focused on developing the concept of unit that is critical for reasoning about spatial and numerical magnitude. The study was conducted with kindergarten students in Russia (N = 105, M age = 76 months). Children were randomly assigned to either an experimental condition, which involved measurement instruction, or a control condition, which involved mathematics lessons on topics covered in regular class instruction. At pretest, participants in both conditions demonstrated little conceptual understanding of measurement, as evidenced by poor performance on an unaligned ruler task. Following the intervention, children in the experimental condition outperformed the control group on this task. Critically, the experimental group also outperformed the control group on three tasks measuring symbolic numerical magnitude knowledge: number line estimation, number comparison, and numeric distance comparison. Thus, the measurement-to-number intervention simultaneously promoted learning in two key areas of mathematical learning that have an overlapping conceptual basis.