EMAT 8990 Research Hulya KilicI think that visualization and spatial abilities are essential to understand geometric facts and concepts. Geometric thinking entails making appropriate connections between the definition of a geometric concept and its representation. However, Clement (1999) noted that prototype descriptions of geometric figures may hinder the development of students’ geometric thinking. He stated that even though children know that a triangle has three sides and three angles, they would name a figure “▲” as triangle but they would not accept “▼” as triangle because it is “upside down.” Vinner and Dreyfus (1989) also pointed out that studentsmay not understand a concept in depth if they do not tie the “concept image” and “concept definition” appropriately. I think that teachers play crucial role in helping students to make such connection between the “image” and “definition” of a concept.When working with preservice secondary teachers I figured out that the weakness in conceptual understanding of geometry and mathematics would lead misinterpretation and misrepresentation of some ideas. For instance, two of the preservice teachers stated that in order to show how ellipses and parabolas are related they would tell the students that an ellipse could be formed by transforming parabolas in certain ways (e.g. They did not give an example but most probably they assume that if one of the parabola passes through (3,0), (-3,0), and (0,2) while the other one passes through (3,0), (-3,0), and (0,-2) then the boundary ofthe region between them would represent an ellipse passing through (3,0), (-3,0), (0,2), and (0,-2). However, if they did check for the accuracy they would see that taken any point except the vertices, lying on the boundary of the region would not satisfy the equation of the ellipse.) Therefore, I began to concern about how teachers could help students to understand geometricconcepts when they still solely base on “the images” they created for those concepts disregarding their definitions. Although pictorial or concrete representation is crucial when 1EMAT 8990 Research Hulya Kilicteaching geometry how teachers could ensure that students would not misconstrue and overgeneralize those representations is worth to investigate. I recommend that teacher education programs should offer geometry content courses and methods course for teaching geometry. One may investigate what course practices help preservice teachers to develop their understanding of teaching and learning geometry. Sub-questions might be: How do they use technology (e.g., Geometers’ Sketchpad, Cabri, applets),manipulatives (e.g., 3D solids, pattern blocks, geoboards), and drawings (e.g., nets, engineering drawings) effectively to teach for understanding? How do these instructional tools help them to make connections between concept image and concept definition? References:Clements, D. H. (1999). Geometric and spatial thinking in young children. In J. V. Copley (Ed.), Mathematics in the early years (pp. 66–79). Reston, VA: National Council of Teachers of Mathematics.Vinner, S., & Dreyfus, T. (1989). Images and definitions for the concept of function. Journal for Research in Mathematics Education, 20(4),