When installed, look for "Without ViewHolder", "With ViewHolder" and "With Cached ViewHolder" icons in your launcher. They are 3 ListViews, with different ArrayAdapter. What's the more efficient?
This app is released under GPLv3, so don't hesitate to look its code, edit it, distriute it and show it in your classrooms. You'll find the explanation and the source at https://github.com/rocboronat/android-viewholder-banana-example
The banana magic icon of this app had been downloaded from http://ztreasureisle.wikia.com/wiki/Emerald_Island and is released under Creative Commons (CC-BY-SA)
And the big picture at Android Market had been found at Wikipedia: http://upload.wikimedia.org/wikipedia/commons/8/89/Green_yellow_bananas_dsc07775.jpg