I was astounded that the effect was so large

From The Marshmallow Study Revisited by Susan Hagen.

The original study, as the article indicates, established that the behavioral trait of self-control is strongly predicitive of life success and that to a significant degree, self-control at such a young age is an innate condition.

In this permutation of the classic experiment, what they have shown is that environmental circumstances also influence the actions of the child.

The Rochester team wanted to explore more closely why some preschoolers are able to resist the marshmallow while others succumb to licking, nibbling, and eventually swallowing the sugary treat. The researchers assigned 28 three- to five-year-olds to two contrasting environments: unreliable and reliable. The study results were so strong that a larger sample group was not required to ensure statistical accuracy and other factors, like the influence of hunger, were accounted for by randomly assigning participants to the two groups, according to the researchers. In both groups the children were given a create-your-own-cup kit and asked to decorate the blank paper that would be inserted in the cup.

In the unreliable condition, the children were provided a container of used crayons and told that if they could wait, the researcher would return shortly with a bigger and better set of new art supplies for their project. After two and a half minutes, the research returned with this explanation: "I'm sorry, but I made a mistake. We don't have any other art supplies after all. But why don't you use these instead?" She then helped to open the crayon container.

Next a quarter-inch sticker was placed on the table and the child was told that if he or she could wait, the researcher would return with a large selection of better stickers to use. After the same wait, the researcher again returned empty handed.

The reliable group experienced the same set up, but the researcher returned with the promised materials: first with a rotating tray full of art supplies and the next time with five to seven large, die-cut stickers.

[snip]

Children who experienced unreliable interactions with an experimenter waited for a mean time of three minutes and two seconds on the subsequent marshmallow task, while youngsters who experienced reliable interactions held out for 12 minutes and two seconds. Only one of the 14 children in the unreliable group waited the full 15 minutes, compared to nine children in the reliable condition.

"I was astounded that the effect was so large," says Aslin. "I thought that we might get a difference of maybe a minute or so… You don't see effects like this very often."

In prior research, children's wait time averaged between 6.08 and 5.71 minutes, the authors report. By comparison, manipulating the environment doubled wait times in the reliable condition and halved the time in the unreliable scenario. Previous studies that explored the effect of teaching children waiting strategies showed smaller effects, the authors report. Hiding the treat from view boosted wait times by 3.75 minutes, while encouraging children to think about the larger reward added 2.53 minutes.

The article focuses on this as being a nature versus nurture issue but I think that is the wrong formulation. I think about this sort of thing in terms of productivity. What conditions favor greater productivity? What this experiment seems to indicate is that 1) Innate self-control is significantly predictive (we knew that already), 2) that teaching habits of self-control can help increase productivity but only in the context of a stable system.

It seems to me that a corolary lesson of this experiment is a powerful endorsement for predictability (i.e. rule of law, systems constrained by checks and balances, etc.). Where there is high predictability, it rewards self-control and therefore more self-control is exercised. The more self-control exercised, the greater the opportunity for investment, experimentation, etc.