After introducing the concept of parallelograms to your class, create a worksheet with 10 or more examples of different parallelograms with the base and height clearly marked. Students find the area of each parallelogram, then move on to another section. In the next section, students find the base and height using rulers. Once finished, ask volunteer 5th graders to share answers and go over any mistakes or questions.
Using a ruler, students cut out paired strips of construction paper with different lengths. Students make rectangles from the strips and use hole punches on the points where the lines meet. Then, students fasten the point loosely together with brass fasteners. Ask students to hold up their completed rectangle and look at the empty space. Direct students to shift two parallel sides away from each other, creating rhomboid shape and look at the empty space. Explain that the amount of empty space is the same in both, only the shape changes.
Draw three differently sized rectangles and section them into boxes like on graphing paper. Provide students with copies of the the rectangles and have them cut them out. Ask students to calculate the area of the rectangles by counting the height and width of the rectangle in number of boxes and multiplying them together. Students cut a right triangle from one side of the rectangle and place upside-down on the opposite side, creating a rhomboid. Explain that the area of the new parallelogram is the same, since there are no more boxes in the new shape.
Distribute rulers and paper to everyone in the classroom. Direct students to look around the room and find five different examples of parallelograms. Using the rulers, students measure the base and height of these parallelograms to find the areas. Write the equation A = b x h on the board, using only the letters rather than the full written form to help students remember the equation's meaning on their own. Students can share examples with the class once finished.