The marshmallow test described here will hardly qualify as a valid scientific experiment. Passing the test won't indicate your kid is on the fast track to Harvard. That said, it is a fun activity to do with your kids, and an opportunity to impart a valuable lesson in patience.
Step 1: The Set-Up
1. Let him/her sit in the chair.
2. Tell them, "If you don't eat that marshmallow in 5 min. I will give you something to go with that marshmallow"(another marshmallow, chocolate, candy, etc.)
3. Once they get that message, leave the room.
That guy below this was really... TEMPTED!