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Abstract: This study explores the process of change of grades 3 to 5 elementary teachers, who participated in a professional development program "Algebraic Thinking: Foundation of Elementary Mathematics". Algebraic thinking as a functional thinking was the centerpiece of the program. The “Concern Base Adaptation Model” (CBAM) was used as methodology. The results of the study showed the significant changes in information, program management and task designing of teachers. Significantly, their understanding about functional thinking progressed. Finally a model was designed for integrating functional thinking in elementary mathematics curriculum as a result of this study.