You have listed several great ways to check understanding in a class like this. Here are a few other examples:
1. With the idea of a practical assignment I would encourage one that has them search for a semi-specific topic (perhaps something like "how to unclog a drain") and do the search in two or three different engines. What was the top page in each search engine? This should help emphasize their search skills as well as the difference in engines. You may also want to vary the exercise by having them use different key word combinations (of their choosing).
2. A self-evaluation checklist. Can I.... search for a topic, type in a specific address, find Amazon.com, etc. People are usually more self-critical than you would be. Review the areas they felt the group generally felt the weakest on.
3. Depending on your environment, you may be able to go back to the learner's after a week and check their understanding with a follow-up task in an email. This may show you points that you need to emphasize in future sessions.
4. Depending on the level of trust among participants they could lead an exercise. Have each of them come up with an example of something they would/need to do (within the context of your class) and lead the group in completing the exercise.
The possibilities are endless really and much will depend on your audience, time available and environment (paid external, internal, volunteer/community, etc.). Good luck!