In this article we examine 4th and 5th grade Portuguese students' performance on problems of structuring 2D rectangular arrays of squares, which was analyzed and categorized into the five levels of sophistication described by Battista, Clements, Arnoff, Battista, and Borrow (1998). In general, the results suggest that students in the higher-grade exhibit higher levels of sophistication. Nevertheless, several students from both grades could not perceive the structure in rows and columns of such rectangular arrays; their spatial structuring of such arrays was still inadequate. The result for their learning may be even worse if we think that for students in these grades, many textbooks display rectangular arrays as the representation to teach area measurement.