The study found associations at r=0.17 for both BMI and educational attainment. Not a lot but not zero.

The marshmallow test deals with kids so it’s noisy by nature, that there are two mild associations is interesting. It has mild predictive value.

I think there’s a strong desire to have this test shown to be faulty. Perhaps because the test is so easy to do, parents do it on their own kids and don’t like the outcome.