Habitat Creation
Have your fourth-graders build their own turtle habitat. Have them fill the bottom of a large aquarium with about 1 inch of mud and some leaf litter. Collect a large amount of pond water and let it sit in an open container in direct sunlight for a few days. After a few days, slowly add the pond water to the aquarium through a strainer. Do not disturb any plants or mud in the aquarium. Once the aquarium is set, you can add tadpoles and other insects along with your domestic (not wild) turtle. Couple this habitat creation with a presentation board detailing in what conditions turtles live.
Turtle Biology
Fourth-graders can create a science project involving the exterior parts of a turtle. They can draw the individual parts of a turtle, such as the carapace (the top shell), the flippers and the plastron (the bottom shell) and then draw a cross-section of the turtle to demonstrate how turtles look when they are inside their shells. Have students draw close-ups of the turtle's head to demonstrate its nostrils, beak and ears.
Cold Water vs. Warm Water
A fourth-grade science project could compare the behavior and growth differences in two turtles which are of the same species when their habitat is warm versus when their habitat is cold. Have your fourth-graders tally how long the turtles spend basking in the sun and how much food they consume and compare that to the temperatures of the habitats. They can demonstrate their findings in graphs and charts.
Turtles vs. Tortoises
An interesting and informative project for fourth-graders would be to have them research the differences between a turtle and a tortoise. Have students explain how the two are similar, such as how they both have scales and both lay eggs, and how they are different, such as how turtles spend most of their time in the water and tortoises are land-dwellers. Have students focus on the diet, habitat, lifespan and biology of turtles and tortoises.