A fun and educational science project on the human eye could be to build a model of it. Different colored clays can be used for the different parts.
By building each specific part of the eye and putting them together to form a complete model of the eye, the builder learns about each part and how they all work together to make the eye function. Parts of the eye to consider including in the model are the iris, the pupil, the cornea and the optic nerve. This is usually the minimum needed to create a basic understanding of the eye, but you can also add more intricate and detailed parts to it if desired.
Each part of the eye needs to be labeled. To explain what each part is and its function, a flash card needs to be presented to go along with each part. When the project is displayed, you need to set the model of the eye on the table and have the flash cards affixed to regulation poster board next to the model. The visual of the model paired with the explanation on the flash cards will give a complete understanding of the human eye that will help your student learn as well as impress judges.