I taught Scratch programming using Arduino robots, to middle-high school level students, during school holidays.
It was quite challenging since I started from scratch, and had to keep several classes interested for a week-long project each.
Kids usually have a short attention span, and you can't afford giving them boring materials, especially when you ask them to work during their holidays.
I started with some programming basics, and quickly moved to the fun part, building their own robots with captors, motors, and programming them to life. It was really rewarding watching them using their creativity to animate a robot. 
The classes were pretty intense as I had to constantly go from one group to another to help them going in the right direction.