The aim of the current research is to develop mathematical proficiency among fifth grade primary students, using a proposed strategy in teaching mathematics based on the six Thinking Hats. The basic research sample consisted of a sample of (92) fifth-grade primary students at Al-Alsun Modern School at East Nasr City Educational Administration / Cairo Governorate (Second Semester), where it was divided into: an experimental group (n = 46), and a control group (n = 46). The study prepared two research tools: the mathematical proficiency test (in the first four dimensions of mathematical proficiency), and the scale of productive disposition (in the fifth dimension); they were applied before and after on the two study groups. The results showed: that the proposed strategy based on the Six Thinking Hats is effective in developing the components of mathematical proficiency represented in (conceptual comprehension - procedural fluency - strategic competence - adaptive reasoning), and in developing the fifth dimension of Mathematical Proficiency (productive disposition) for Fifth class primary students. Key words: The Six Thinking Hats - Mathematical Proficiency - primary school students.