Fourth grade inventors like things that go fast, so creating running shoes that speed up a runner is an appropriate project. Running shoes that go faster require the use of springs and two wooden platforms. Trace a shoe pattern on a 3/4-inch piece of plywood or other wood you have around the house. Attach springs in between the two pieces of wood using wood screws and brackets. Tape the spring platforms onto a pair of running shoes with duct tape and test your theory. Students should compare the results of the invention for both speed and distance and record their results.
Fourth graders like to make everyday jobs easier. A light switch that you can turn off from your bed does just that. Attach a small pulley to the light switch using screws. Thread a string through the pulleys and attach it to the switch with a clip. Stretch the string over to your bed. When you pull the string, the light turns off.
Kids like dunking cookies into milk, but often their fingers get dirty from the cookie or wet from the milk. To solve this problem, use a simple crank system. For this invention you need a wooden dowel rod with a "v" notch cut into the end, and wooden wheel and some kind of simple axle. The cookie rests on the notch and when the wooden wheel is turned, the axle lowers the cookie into the milk. Attach the entire crank system to the side of a glass with a clip or a clothes pin.
Mopping shoes are a simple fourth grade invention that helps improve the floor mopping experience. This happens because the mops are attached to the shoes which prevents having to bend over to mop and also provides some exercise for the use. For this project you will need two large sponges and some strong adhesive. Place the sponges under the shoes and trace the shoe pattern onto the sponges. Cut out the tracing and attach the sponges to the shoes using some type of waterproof adhesive such as super glue.