This chapter argues that visual-spatial thinking in primary school mathematics education should not be treated as a limited skill associated only with geometry learning, but as a central cognitive resource in the construction of mathematical understanding. In the early grades, students often make sense of number, measurement, patterns, geometry, problem solving, and mathematical modelling through visual representations, spatial relations, orientation and position awareness, mental transformation, comparison, estimation, and concrete experiences. Accordingly, visual-spatial thinking should be considered not merely as a supportive element in mathematics instruction but as an integrative structure that enables students to connect, explain, and transfer mathematical concepts across contexts. The chapter first discusses the theoretical foundations of visual-spatial thinking and then examines its relationship with mathematical understanding from developmental, pedagogical, and interdisciplinary perspectives. Piaget’s theory of cognitive development, Vygotsky’s sociocultural theory, visual-spatial working memory, representational transformation, and embodied cognition constitute the main theoretical basis of the chapter. In addition, classroom-oriented examples are presented, including the prediction-observation-comparison cycle, the use of visual representations, orientation and position activities, measurement and comparison tasks, pattern and symmetry activities, and interdisciplinary learning experiences. The chapter concludes that systematically supporting visual-spatial thinking in primary mathematics education may deepen students’ mathematical understanding and provide teachers with a more inclusive, multi-representational, and interdisciplinary instructional framework.