Sometimes the best way to teach students a new concept is to let them figure it out for themselves. Give students rulers or tape measures that contain both U.S. and metric measurements. Set them loose in the classroom to measure various objects and lengths, such as desks, chairs, windows, walls and anything else. Instruct students to write down their measurements in both U.S. and metric figures. Challenge students to try to come up with a formula for the conversion. While fourth grade students will probably not be able to do this, just the attempt will be a worthwhile exercise.
Part of learning metric conversion involves memorizing the relationship between U.S. and metric measurements. After teaching your students equivalent measurements, such as 1 inch = 2.54 centimeters and 1 kilogram = 2.2 pounds, write measurements out on index cards. Write one U.S measurement per card and make sure its metric equivalent also has a card. Put the cards on the floor and have students play a memory game. Students take turns flipping over two cards at random. If they find two cards with equivalent values, they get to keep the cards and get a point.
Another way to teach metric conversions to fourth graders is to give them situational problems that ask them to convert units. For example, give them a word problem where someone needs to drive 15 miles, gets 10 miles per gallon of gas and has 5 liters of gas. Have students figure out if the person has enough gasoline to get to his destination.
You can also use students' creativity to teach metric conversion. Have students design their dream house or room by making a floor plan. Tell them to include furnishings, such as desks, beds, computers, televisions and anything else, perhaps even a swimming pool. Have students calculate the measurements for their dream house or room in both U.S. and metric figures. Have them verify that their conversions are correct.