In a training course:
Provide 2 glasses of the same size. One is filled with 100 marbles, the other one is empty.
The goal during the course is, to shift the marbles from one glass to the other.
Provide some rules that allows one participant to move one or more marbles from one glass to the other.
If you do training courses with a lot of activities where groups have to create something, like a flip chart, or a presentation to teach others in the class you can rate the results and give one to five marbles to the team.
Or you can reward cool statements from participants or even cool questions with marbles.
This has the effect, that people try to participate more to get more marbles to finish the challenge :)
The course wins, when all marbles from the first glass have been moved to the second one.
Maybe reward everybody with small gifts, like coaching cards or similar items.