The purpose of this study was to explore Grade 4 students’ understanding and examine the difficulties they encountered in representing the area of rectangles. The sample consisted of 33 Grade 4 students from Sathit primary school. The instruments used for data collection were activity sheets and students’ group explanations. The collected data were qualitatively analyzed through a categorization of students’ responses. The findings revealed that most students demonstrated a sound understanding and were able to classify different types of rectangular shapes effectively. Through the activities, students were able to identify the characteristics of rectangles, determine their areas, and derive formulas for calculating the area of rectangular figures. However, some students experienced difficulties in categorizing shapes, particularly confusing the longer side with width and the shorter side with length, which resulted in incorrect substitution of numerical values for length and width. Additionally, students showed confusion in distinguishing between the units of length and of area. These findings suggest that students need increased attention to detail when identifying geometric shapes, distinguishing between length and width, and recognizing the appropriate units for each measurement type, as well as correctly substituting values into formulas