Marshmallow Bleg

I think the answer is no. The way to get a definitive answer is to ask Walter Mischel, who is at Columbia.

There was a follow-up study that he co-authored recently, but it didn't look at income. That follow-up is "Behavioral and neural correlates of delay of gratification 40 years late."

It references some other literature on this topic: "Previous research has documented that higher delay ability promotes the development of better social–cognitive and emotional coping in adolescence and buffers against the development of a variety of dispositional physical and mental health vulnerabilities in middle age, such as high BMI, cocaine/crack use, features of borderline personality disorder, anxious overreactions to rejection, and marital divorce/separation." I suspect those references would be a good place to start, but I don't think you're going to find anything.

If you broaden this to childhood/adolescent non-cognitive skills of various sorts and adult outcomes including income, there is literature, including literature that conditions on aptitude test scores. (Heckman has done work on this with NSLY79.)

Link: http://www.pnas.org/content/108/36/14998.full.pdf

What if the child preferred to eat only one marshmallow in the first place?

By coincidence, half an hour after reading this blog, I read this in Steven Pinker's The Better Angels of Our Nature, pp722-723:

Walter Mischel began his studies of delay in gratification ... in the late 1960s and he followed the children as they grew up. When they were tested a decade later, the ones who had shown greater willpower in the marshmallow test had now turned into adolescents who were better adjusted, attained higher SAT scores, and stayed in school longer. When they were tested one and two decades after that, the patient children had grown into adults who were less likely to use cocaine, had higher self-esteem, had better relationships, were better at handling stress, had fewer symptoms of borderline personality disorder, obtained higher degrees, and earned more money.

His references:

Metcalfe, J. & Mischel, W. 1999. A hot/cool system analysis of delay of gratification: Dynamics of willpower. Psychological Review, 106, 3-19

Mischel, W., Ayduk, O. et al. In press. 'Willpower' over the life span: Decomposing impulse control. Social Cognitive & Affective Neuroscience.

It's funny how the ethnic aspect of this series of studies gets forgotten:

"The experiment has its roots in an earlier one performed on Trinidad, where Mischel noticed that the different ethnic groups living on the island had contrasting stereotypes of one another, specifically, on the other's perceived recklessness, self-control, and ability to have fun.[5] This small (n= 53) study of male and female children aged 7 to 9 (35 Negro and 18 East Indian) in a rural Trinidad school involved the children in indicating a choice between receiving a 1c candy immediately, or having a (preferable) 10c candy given to them in one week's time. Mischel reported a significant ethnic difference, large age differences, and that "Comparison of the "high" versus "low" socioeconomic groups on the experimental choice did not yield a significant difference".[5] Absence of the father was prevalent in the African-descent group (occurring only once in the East Indian group), and this variable showed the strongest link to delay of gratification, with children from intact families showing superior ability to delay."

http://en.wikipedia.org/wiki/Stanford_marshmallow_experiment