This explanation unit uses Until I Met Dudley by Roger McGough as an example, then children write their own explanations inspired by Wallace and Gromit’s Cracking inventions.
Many other good explanation texts can also be found by following the above link. These would make useful Guided reading books and provide additional examples.
The series of Wallace and Gromit ‘Cracking Inventions’ can be found at; http://www.youtube.com/watch?v=6cxAuU5nReU
For this unit, I’d suggest the video clips; The Snoozatron, The tellyscope and The soccamatic . However, there are lots to choose from which should allow for effective differentiation when planning the final written outcome.