Pour 1/2 cup white school glue into a bowl
Add 1/2 cup water and mix well
Add a few drops of food coloring if desired
Stir in 1/2 teaspoon borax dissolved in 1 cup warm water, or add liquid starch slowly
Mix until the goop starts to form and pull away from the bowl
Knead the goop with your hands until it is smooth and stretchy
Add a little more activator if it is too sticky
Add a little more glue if it is too stiff
Store in an airtight container when not in use