This paper presents an investigation of the geometric thinking of the preservice primary teachers. One hundred forty-five preservice primary teachers, with diverse mathematical background, in three different programs were tested for their van Hiele levels of thinking and language structure in geometry. In order to answer meaningfully and effectively the how much or what extent type of questions, we found the effect sizes and made use of power analysis. Much of this study concurs with previous researchers on the van Hiele Theory. Many preservice primary teachers lacked correct basic definitions and used Level 1 type language. Most of them needed Level 2 (Analysis) and Level 3 (Informal Deduction) experiences to provide a foundation for their geometric reasoning.
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CONCLUSION AND IMPLICATIONS
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