If they don't help, they're not trying to increase productivity.
If they DO help, their OWN productivity will suffer, and if they are truly in, say, the 10%, they are probably more productive than a newbie will ever be.
The problem is that the boss needs a way to tell if that help is falling on deaf ears. If the help isn't having a sufficiently positive effect, then you have someone who is not qualified to do the work. Is the boss really interested in making his team stronger all-around (not just a few star employees), or does he just not want to have to deal with answering questions from new hires who might be struggling?
I'm in this position right now. I'm not being conceited, but I am in the role of the highly-productive employee. My boss hires people (or we acquire new team members as the result of a company organizational change). Either way, before the new team members start, my boss inevitably asks me to make sure they can do the job. I've never seen anyone in my department fired due to incompetence. Whenever a team member has questions/problems, they almost always end up getting sent to me. It has gotten to the point where I now have to head a weekly developer meeting that is really just a glorified question and answer session.
The problem is that my team members are never weaned off of my help. My boss doesn't seem to care about this. I've overheard him say to people, who were trying to figure things out without having to ask me for help, to just ask me. I understand that it's more important to my boss to just get things done, but that creates an unnecessary dependency on me. I'm not scalable. Hire better employees or take a hands-on approach to training, but don't keep sending them to me all the time.
I can understand why the author's top employees didn't want be bothered with helping those who were struggling. You don't want to be in a position where you have to do your job plus some/most/all of someone else's.
He takes the blame, but he also realizes the cause of the problem and does nothing: "particularly given that we keep track of everyone’s output and any time spent teaching new people would reduce the build total of the teacher."
Yeah, that really stood out to me. He claimed to want to train the new people, but also said he couldn't afford the loss in productivity. You can't have it both ways.
We told the veterans to help the new people whenever they could, but none of the old heads really wanted to be bothered
But that contravenes:
Employees will try to increase productivity in operations whenever possible.
He's got them all over a barrel.