Bring 1 cup of water to a full boil in a small saucepan or kettle.
Pour the boiling water into a heat-safe measuring pitcher, then add the Jell-O powder and granulated sugar.
Stir steadily until the gelatin and sugar are completely dissolved and no grains remain at the bottom.
Add 1 cup of cold water and stir until evenly combined.
Place the popsicle molds on a flat tray and pour the mixture evenly into the molds, leaving a small amount of space at the top.
Insert the mold handles or popsicle sticks and transfer the tray to a level freezer shelf.
Freeze for at least 4 hours, or preferably overnight, until the centers are completely firm.
To release the popsicles, run warm water over the outside of each mold for several seconds, then pull gently and straight upward.
Serve immediately and keep the remaining popsicles frozen until needed.