Moodle provides a wide array of options for self-paced independent study students to demonstrate achievement. We've recommended using certificates and badges because the process of earning, issuing, and displaying them can be automated.
Motivation through setting goals and then rewarding people when they achieve the goals is at the heart of badges and certificates.
In the case of badges, there is an element of gamification, which encourages students to compete with each other to earn badges and be the best in terms of their respective skill sets and interests. We have discussed badges and certificates and it's useful to review them and remind ourselves that they both motivate while the course is in progress and when it is complete.