Maintainability is a major stake of professional software development. Indeed, maintenance is nearly always the longest part of a software life cycle, as it lasts from the project release until basically the end of times.
Moreover, projects being in maintenance represent a large majority of the overall number of projects. According to http://www.vlegaci.com/298/interesting-statistics-%E2%80%93-numbers-of-programmers-in-maintenance-vs-development/, the proportion of projects being in maintenance is about 2/3.
I recently came across this question, where the guy looks pretty surprised discovering that his job is mainly about maintenance. I then decided to open a discussion (french) on the main site of the French community of software development professionals (http://www.developpez.com/). The discussion is entitled "Are students well-enough trained to the reality of professional software development?" and is mainly about maintainability. It was pointed out that, at least in France, people are not well-enough prepared to face maintenance in both aspects of it:
- maintain existing code
- make maintainable code
My question here echoes to this discussion and aims at finding a good way to teach maintainability.
- How can we teach maintainability?
- What kind of exercise would you suggest?
- If you have been well-trained regarding maintainability, what particular kind of courses did you take?
 After some misunderstanding, I think I must clarify my question. As a project leader and software developer, I often work with trainees or freshly graduated students. I once was freshly graduated myself. The thing is that students are usually unfamiliar with principles such as SOLID that increase the maintainability of a project. We often end up having important difficulties making projects evolve (low maintainability). What I am looking for here is a concrete academical example of successful teaching about the importance of maintainability and how to make better code regarding this particular point; or possible suggestions to improve the way students are trained.