When students fill rectangles with square crackers, what does the number of crackers represent?

The number of square crackers used to fill the rectangles represents the area of the rectangle. Area is defined as the amount of space contained within a two-dimensional shape, and in this case, each square cracker represents one unit of area. When students place the square crackers inside the rectangle, they are essentially covering the entire surface area of that rectangle, which is calculated by multiplying the length by the width of the rectangle. Thus, counting the number of crackers gives a direct representation of the area, demonstrating a practical understanding of this geometric concept.

Regarding the other alternatives, perimeter measures the distance around the rectangle, volume relates to three-dimensional space, and the length of the sides provides dimensions but does not account for the full area covered within the shape. These concepts are distinct from area, which is specifically what the square crackers illustrate in this scenario.