The effects are real, but not miraculous. The first thing to note is that across the whole group, the improvements in both cognitive skills and noncognitive skills are positive and nontrivial, but not huge, either: about a tenth of a standard deviation on cognitive skills, about two-tenths that for noncognitive.
The actual study:
The impact of being offered a chance to participate in our parental incentive scheme
on non-cognitive skills is large and statistically significant (0.203σ (0.083)). These results are consistent with Kautz et al. (2014), who argue that parental investment is an important contributor to non-cognitive development.
(Black students showed no improvement.)
Hispanics (48 percent of our sample) and Whites (8 percent of the sample) demonstrate large and significant increases in both cognitive and non-cognitive domains.
Nobody can do anything ever!