"You find that the way that the children generally do it is they come up with some sort of strategy to get through the delay.
"You have got the singers, who sit there and start singing to themselves.
"You have the children who crawl under the table or turn their chair around so they don't actually look at the reward.
"We have children who use the chairs to set up a bus."
Then there were some children who go for the one marshmallow - or sticker - right away.
Children who have taken part in a variation of the marshmallow test, with marshmallows substituted for stickers, will be tested again after they go back to school.
"At the moment, we know that children's performance on the marshmallow task relates to aptitude in schools.
"What we don't know is whether the strategies is what is contributing to that."
His lab now has an eye tracker, which gives a more sensitive reading of what pupils are focusing on in order to avoid being tempted.
A study he and other researchers, including vice-chancellor Prof Harlene Hayne, published earlier this year found if 3-year-old children had the implications of their decision brought to their attention they were more likely to exercise self-control.
Parents of young children interested in taking part in the research could contact Dr Scarf at: damian@psy.otago.ac.nz