But read further down on the details and that difference disappeared almost immediately after the end of the intervention. It follows in line with a well known fact that childhood IQ is primarily driven by environmental factors whereas adolescent and especially adult IQ is primarily driven by the IQ of your parents - paradoxically, strengths or deficiencies in earlier life notwithstanding.
And their decision to set the baseline for arrests at 5+ is obviously doing something akin to p-hacking. It makes it clear that near 100% of the entire sample (males at least) ended up in prison, likely multiple times. The ROI from the program had nothing to do with increased productivity - it was driven almost entirely by less time spent in prison. It led to the interesting fact that 93% of the ROI came from males, precisely because the females had a much lower baseline criminality rate.
In a nutshell, the main benefit of the program was reducing the criminality rate of the experimental group to a level that is still orders of magnitude higher than for society at large. That is a good thing, but it also emphasizes that something like this would only be the beginning of special care needed to try to ensure these sort of people could live remotely decent lives.