Have you heard of it? The "official" test is suppose to be given when a child is 4 years old. They are given one marshmallow and told that if they don't eat it when the adult returns, they will be given two marshmallows. They are left alone for 20 minutes.
We did M&Ms and Sally was left for 3 minutes. Check out the video and see if she can delay gratification or if she needs it instantly :)