[x SF med]

Bill-
The organic changes to the brain caused by prolonged (or just excessive single dose) drug use, especially alkaloids, opiates and lysergines is generally not considered reversible - once brain cells are dead, they're gone. The brain can be repathed through intensive training/therapy - but the actual sections of the brain that are damaged will always be damaged.

Meth is especially evil in this respect due to the compounding effect of the chemicals used in manufacture, and the way meth affects the total nervous system. As a short non-scientific answer, meth attacks the higher thought centers and the 'control' centers (both voluntary and autonomic) of the brain.
Another effect of meth is the onset of psychosis in long term use, including bipolar disorders, straight depression, and hallucinatory/ paranoid disorders.
It's bad shit. Since these kids were (I suppose) heavy users at a young age, the effect is devastating, the brain may have ceased to develop, and there are probably mental and emotional components to the developmental retardation on top of the stated cognative issues.

Had Meth been the big thing in the 60's you'd have the term "meth casualties" instead of "acid casualties".

If I seem a bit in tune with this, it's because my older brother did this to himself - in his 20s, as a Marine (prior to drug testing) wit ha combination of LSD, pot, PCP, alcohol and the corrosion control chemicals he was exposed to in his job - my bet is the 10 hits of acid, 2 cases of beer and the dusted joints (according to him, nearly every night) did a great majority of the damage he's still trying to overcome decades later.

Your friend may be able to help one or two of these kids, the lightest of the former users, but even that is going to be an uphill battle.

God bless him for his efforts, but from experience I know how frustrating it is to see all that potential gone to waste.