A discipline anecdote:
When I actively taught swimming at a YMCA, a local university contracted with us to teach swimming to a group of children with severe behavior problems. The fella (call him Joe) running the program was working on his Phd & the kids were the subjects.
We instructors first had to meet with Joe in order for him to instruct us on how the program worked. Essentially it was based on a reward system with no punishments. Every child received gold stars for doing even the slightest thing 'right', such as brushing their teeth, following an instruction etc.. In order to get to do anything outside normal routine, the child had to have earned a certain number of rewards.
I saw very few bad behaviors by these children, but then if they were even in class it was because they had earned it with good behaviors.
I think overall, each individual case needs consideration on its own merit & that sometimes punishment is called for when other methods fail. I think people in prison need work of some kind to do so that they learn to discipline themselves as well as contribute economically.
