Headline seems accurate to me. The headline: New Study Disavows Marshmallow Test’s Predictive Powers. And it does. The marshmellow test as a single measure

Headline seems accurate to me. The headline: New Study Disavows Marshmallow Test’s Predictive Powers. And it does. The marshmellow test as a single measure is referred to as RND. Which is a test which measures gratification wait times and is applied in pre-school. Their hypothesis regarding RND: hyp2: On its own, RND (measured around age four) will have only a very small correlation with the measures of mid-life capital formation. And they report a confirmation of this hypothesis. The other hypothesis refers to RNSRI rank-normalized self-regulatory index - which is 4 different components measured at different ages - each component is RND + 86 other measures! This is reported as having a "modest" impact on outcomes - not "strong" as you say. So your reporting seems the more inaccurate to me. But this is irrelevant anyway with respect to your claim about the headline, which is only referring to the paper's disavowel of RND. Further evidence of the headline's accuracy and the paper's disavowel of RND is that they also looked at RNCCQ - which is RNSRI minus the inclusion of the RND test from each of the four components. They found that including RND did not improve RNSRI over RNCCQ in terms of their predictive power.