I'm not sure how apprentice training in this respect is done in the US, but here in New Zealand, all apprentice Line Mechanics are sent to one of the National Lines Colleges.
Here, they teach Line Mechanics the basics of Line work, all the theory and practice required to start out as a trainee.
They actually have a whole series of made up Line Networks and Substations, spread over a few acres and they can be dead or livened as the need may be.
I would give you a link but most of them can't afford to have Internet sites.
However, most of us Line Mechanics have been to these Colleges more than once and I really enjoy the courses.
But back to your question, sure it is a Catch 22 situation, but, a lot of this comes down to supervision and knowing exactly what the apprentices skill level and general aptitude is like.
And also, with a trainee on site, I'd personally make it known exactly what the work involves and each step of the job, so that there is no confusion whatsoever and no chance that the trainee could be in the wrong place at the wrong time.