At my company we put a big emphasis on code reviews. We encourage devs to pull request code fairly regularly to keep PRs relatively small (when possible) -- before so much code has been written that it's not really possible to change course without blowing up deadlines. We encourage our junior devs (who might not be capable of identifying bugs or proposing fixes on code written by a senior) to ask questions in their code reviews -- to verify assumptions, to request an explanation of how something works, confirm that a particular edge case has already been considered, etc. It can be hard to get a junior dev comfortable with doing this (questioning a senior dev), but even if the junior isn't identifying bugs it will often lead the senior to better understand their own code and the architectural concepts that underpin their own coding decisions. Like the author points out, this only happens because the senior dev endeavors to explain their work to the junior dev (Protege effect). Also, a good many times it leads the senior dev to re-consider how they wrote something and they might add a revision to address a possible edge case not previously considered. I hadn't thought of it this way before, but this is the Socratic method that the author talks about.

We also put a big emphasis on in-code comment writing -- largely following the commenting principles laid out by John Ousterhout's "A Philosophy of Software Design". These comments are of course for long-term maintenance purposes, but they also benefit team learning. Class, method and variable naming are obviously important too. Our internal code reviewing mantra is that 'I want to be able to read your code like a story book -- when I get to the end, I at least want to be able to understand what happened'. Not always possible, but a good goal. Writing comments and choosing class/method/variable names in pursuit of that goal massively contributes to the learning of the team. During our code reviews, one of the most common requests by reviewers is for the author to add a comment explaining something that was very difficult (or impossible) for the reviewer to grasp on a first read.

This approach has worked very well for us. Everyone learns and our product quality improves.