I'm a bit at a loss at the resistance to the idea of the comparison of aikido and educational systems.
Piggybacking on Carsten's post. The practice is goal not a means to a goal. Tests and rank aren't why I attend class. I attend so I can practice. The act of practice is what is enjoyable and fulfilling.
Although they have advanced in rank over the years there are multiple people in the dojo I attend that have been there 20+ years. They aren't trying to "graduate", they just like the practice.