Place a sheet of foam poster board with the shorter sides turned vertically. Cut the poster board in half from top to bottom. Turn the two boards so the shorter sides are vertical.
Place an 8-by-8-inch square sheet of sandpaper with the rough side facing up on the left side of one of the poster board rectangles. Position the sandpaper so it is square with the poster board and 1 inch away from the leftmost side. Affix the sandpaper square to the poster board with hot glue.
Position the remaining poster board with the short sides turned horizontally. Arrange five 8-by-2-inch rectangles of sandpaper horizontally down the length of the board. Place the rectangles in order from smoothest to roughest. Space the rectangles evenly apart. Attach the rectangles with hot glue.
Instruct your child to rub her fingertips over the smooth and rough textures of the first board. Ask her to feel the difference in the gradients on the board with five types of sandpaper. Increase her sense of touch as she detects the differences between the smooth and rough surfaces and the degrees of roughness.