[netjiro]

> study done on kids that I wish I had the source for.

There are a lot of them with similar results, going back to 1960s.

Kohn "Punished by Rewards" is a good general start for that stuff. I think there was some generalised study/review published in late 90s. Probably Deci and Ryan (?).

[kqr]

Also Pink's Drive has a lot more on the research around motivation. Highly recommended for anyone working with people, or having children.