Cut off a 6-by-6-inch square of cardboard with a pair of scissors. Place this cardboard on a clear work space, preferably one near a sink in case of a spill. Cut off the top 2 inches of the 2-liter bottle, then place the bottle in the center of the cardboard square, open side up. Tape the bottle onto the cardboard with duct tape.
Instruct the student to make the slopes of the volcano by cutting strips of cardboard and taping them to the side of the volcano. So long as she does not build over the top of the bottle, let the child explore her creative and artistic side by making the volcano however she wants. Show her pictures of real volcanoes for ideas. Let the child determine the slope of the sides and decorate it with markers. Let her make rocks by crumpling cardboard.
Give the student a notebook and make three columns. One column is for the constant variable, which will be one teaspoon of vinegar. The second column is for the independent variable, which will be a dynamic amount of baking soda. The third and final column is for the dependent variable, which will be the size of the eruption.
Pour one teaspoon of vinegar into the bottle and then have the student add baking soda in the amount of her choosing. Have her record her observations on the eruption. The amount of experimental runs will depend on the grade level, generally with more runs for the higher grades. Require the student to record all the runs herself.