The purpose of this study was to investigate the effects of geometry instruction emphasizing relational understanding on preservice elementary teachers’ geometric thinking levels. Four groups of Basic Mathematics II were selected as the sample. One of the groups received traditional instruction and the other three groups received geometry instruction which emphasized relational understanding. A pre-post test experimental group design was used. After 5 weeks instruction, it was found that there was a significant difference between the geometric thinking levels of the experimental and control groups in favor of the experimental group. In addition, there was a significant difference between the pre and post test geometric thinking levels of the experimental groups.

Keywords: van Heile geometric thinking levels, preservice teacher education