Find a spot in your classroom where the sun shines directly through a window. Gather all of the children in this sunny spot and discuss how the rays of the sun are shining through the window. Tell them that you are going to add another boundary for the light to shine through, which will bend the light into seven different colors.
Have one child fill the glass about halfway to the top with water.
Place the glass of water in the direct line of sunlight and the white piece of paper on the floor where the rays ultimately end.
Show the children that the light shining through the glass of water has refracted and separated into seven different colors of the spectrum, or a rainbow. To help children remember this experiment, have them draw the steps you took to create the rainbow, or refract the light.