"This new paper found that among kids whose mothers had a college degree, those who waited for a second marshmallow did no better in the long run—in terms of standardized test scores and mothers’ reports of their children’s behavior—than those who dug right in."
Since "standardized test scores" tends to measure IQ, it seems this can be re-phrased as "those who did well on the will-power test did not necessarily do well on the IQ test, and vice versa."
In other words, raw will-power is not correlated with raw IQ. Which I think I already knew? I've certainly known some athletes who were probably not as smart as me, but who definitely had more will-power than me.