Does the one that won't learn have a dislike of learning and/or work? If so you may have to stay there keeping a good eye on him for quite sometime before he'll learn enough to stay there on his own and even then he may walk away more than others. As far as the fishy problem you will have to just keep bringing them back to their job when they wander off to do that. Just put them on a job and they shouldn't go away for a little while. That's about all I can give you.
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Things may seem grim and down, but if you wait it out often things will often appear in a new light.