People who have never been in prison probably don't picture how a real inmate looks like. Even in movies today, stereotypically, prison inmates are just big, strong, scruffy, and curse a lot. Even stereotypically, a prison inmate is much worse. Actually seeing some prison inmates is scary. These guys are ugly both inside and outside. They have no regard for anything. One guy is even quoted as saliva is sliding down his chin, they "will eat you alive."
In this documentary these corrupted teens, some as young as the age of ten, are yelled at only inches away from these "monsters." They are constantly harassed. For instance, one kids name is changed temporarily to Bridgette, and another kid must follow an inmate very closely holding the inmates shirt. This simply strengthens the reality that if these children end up in one of these prisons, there will always be inmates, bigger, stronger, and nastier than them, and no one is there to save them.
At the end of the movie, the children reported back on how their behavior has been. Out of about fifteen kids, all but one reported that they have not done anything troublesome. Clearly this technique, which has caught on to shows such as Jenny, Ricki Lake, and Sally, has been working effectively, and maybe eventually kids will not have to be Scared Straight.