How to run programming/hacking workshops?

I'd love to hear about strategies for running workshops and other experiential-based group learning models.
- How do you balance structured lessons and worked out examples with unstructured hacking time?
- How do you create a conducive environment for students to collaborate and help each other?
- How do you keep everybody focused?
- How do you integrate online back channels, e.g. etherpad, IRC, github?
- How do logistics affect the workshop, e.g. number of students, number of teachers, length of session(s), venue?
- How do strategies change with participants of various ages and backgrounds?
- How do you evaluate the effectiveness of the workshop?