I am working as a volunteer, teaching children programming once a week.
The attendence is somewhat irregular (and the children are a bit restless :P) so, instead of more traditional lectures, we try to give the children self-paced activities at the computer.
This class is goes on for 1hour 20mins, in which we usually have the students trying to complete a series of "programming challenges" aimed at teaching a particular concept.
Often, however, children get tired in mid activity. What can we do to re-energize the children? How long is it resonable to expect an activity to hold a child's attention?
(ages: 11 up to 15. But mostly 11 and 12)