This study explored 5-6 year-old children's conceptual understanding of one geometric shape, the triangle. It focused on whether children could draw a triangle from memory, and identify triangles of different types, sizes, and orientations. The data were collected from 82 children attending state preschool programs through a one-on-one interview, during which children completed five paper-pencil tasks. Findings showed that the majority of the children (93%-96%) successfully identified a prototyped triangle. Approximately half of the children experienced difficulties in identifying triangles of different sizes, types, and orientations. The most difficult area was identifying types of triangles, where an isosceles triangle and a right triangle were presented, followed by identifying triangles in different orientations, specifically flipped and rotated ones. Children appeared to identify and classify the triangle relying on the visual prototype. These findings provide support for the Prototyped Theory, van Hiele theory, and for works by Clement and colleagues. (author abstract)