I did this project when I was a kid..."Will a plant grow through a maze if light is its reward?" Basically we used a liquor box with the cardboard dividers. Put a plant in one corner, and cut holes in some of the dividers to make a maze, ending with a hole in the opposite corner for the light to come through. Water the plant normally, put it in a window with the hole facing the window to get optimal light. Let her measure it with a ruler (or use pieces of yarn once a week for a good visual, tape them to the presentation board labeled with "week 1" etc so the kids can see). Message me if you have specific questions. This one is simple and can be inexpensive. (I would highly recommend covering the outside of the liquor box with some kind of wrapping paper. hehe)