The egg drop project is a fun science project for fifth graders that encourages creative problem solving strategies. Using household items, the goal is to create a system that will protect the egg when dropped on the ground.
Another idea would be to test different plant-growing products. Buy three plants and two different
plant-growing substances such as Miracle Grow. Just use water for one plant and nutrients for the two other plants. This project tests which of the plant nutrient products works best and gives the student a better understanding of the scientific process. By just using water on the first plant you've established a control, so any difference in the other two plants can be attributed to the plant supplement. Both of these projects are not only easy enough for a fifth grader but also teach valuable science lessons.