Understanding quadrilaterals, as one of the more challenging topics in geometry, is influenced substantially by the content of mathematics textbooks, particularly at the elementary level. The purpose of the present study was to examine the progression of content related to quadrilaterals and the corresponding Van Hiele levels of geometric thinking in elementary mathematics textbooks, in order to explore the extent to which these materials reflect the levels of thinking expected from students. The study employed a descriptive–analytical design with a qualitative approach. Relevant sections concerning quadrilaterals were purposefully selected from the textbooks. Data were collected using content-analysis forms based on Van Hiele levels, whose face and content validity were confirmed by experts in mathematics education. Inter-rater reliability for the coding process was ensured using Cohen’s kappa coefficient. The findings indicated that the presented content includes the introduction of names and visual representations, prototypical examples, drawing methods, hands-on activities and construction tasks, properties related to sides, angles, diagonals, and symmetry, hierarchical or partition-based relationships, and the sum of interior angles. This content corresponds to Van Hiele levels 1 through 3, with level 2 being the predominant level. In terms of content progression, squares and rectangles are introduced for the first time in grade one, while trapezoids, parallelograms, and rhombi are introduced in grade four. Moreover, none of the quadrilaterals are formally defined using the term “definition,” although the presentations in the grade four textbook are more closely aligned with formal definitions.