The quote at the end of the article tells you what you need to know about the rest of the research. This is where she wanted to go all along:
Instead of limiting ourselves to narrow standardized tests, we might seek as well directly to assess motivation as well as creativity, practical skills, wisdom, and even ethics. If we did, we might find our society advancing to levels of economic productivity and, for that matter, well-being that we previously believed to be out of reach.Yes, and boo'ful kitties as well.
I have little doubt that the study tells us a little something, but not quite what Duckworth thinks. That motivation influences scores is rather obvious, but perhaps it does need to be studied and teased apart a bit. Here's the thing: high motivation doesn't raise one's score much, but low motivation can certainly depress it. Thus, when the films are reviewed for sign of ebbing interest, they are picking up the losses. If one transfers thinking about this over to athletics, my statement about motivation becomes clearer. A good athlete, with training, he might cut as much as minute off his time in the mile run. If motivated by a coach, a drill instructor, a competitor, or a corny movie, might cut 10, 20 seconds off his best time during that training, especially at the beginning. And that's it.
But a less good athlete can lose a lot more than a minute by being unmotivated. He can slow to a jog, or even a walk, completing the task only for politeness or because others are yelling. In fact, it will usually be the less good athletes who do this, and the poor athletes most of all. The bad singers will get quieter, try to turn invisible, not show for practice. Unskilled artists will try to just get out with a dashed-off sketch. People like succeeding at things, and so keep doing things they are good at. Things they aren't good at, they will focus on less, unless there is some other draw - social, monetary, guilt.
This is surprising? Is this the great new knowledge in understanding IQ scores, that the kids with 120 IQ and above will fight for every point, while the kids at 85 may blow off subtests they are particularly bad at and drop to 81?
It seems a strawman that Duckworth is arguing against, that there were people who viewed IQ tests like a Sorting Hat, a smart-o-meter that reads your brain wand the dial hits a number installed at birth? Has she met such folks? There are people who take the stability of IQ more seriously, much more seriously, than Duckworth does, and have evidence to back it up. She hasn't dented their view with this.