Set out heat proof glasses. You will need six of them.
Combine one package of jello with one cup of boiling water in a large heat proof bowl. Whisk until the jello has fully dissolved. Whisk in one cup of cold water.
Carefully pour equal amounts of the mixture into each of your serving glasses. Carefully transfer the glasses to the fridge to chill until fully set, about 2 to 3 hours.
Once the first layer has set, remove the glasses from the fridge.
Whisk together another package of jello with one cup of boiling water until jello is fully dissolved. Add one cup of cold water and half of the cool whip (4 ounces). Whisk until combined. Carefully transfer equal amounts of the mixture into each of your serving glasses.
Transfer the cups to the fridge to chill for another 2 to 3 hours until set.
Once the second layer has set, whisk together last package of jello and one cup of boiling water. Once the jello has dissolved, whisk in the last cup of cold water. Carefully pour the jello into the cups, dividing equally among each of the glasses.
Transfer the jello to the fridge to chill for another 2 to 3 hours.
Just prior to serving, top off each of the jello cups with the remaining Cool Whip. Garnish with sprinkles and serve chilled. Leftovers can be stored in the fridge for up to 2 days.