I have been working on writing a scheme of work for ICT for students between P1i-P8 which is a mammoth job! However I have come across some useful things while writing it. I may make some of it available if I can link to this blog.
Inclusive Technology have written a switch progression road map which is a must have for anyone working with students between P1i and P6.
The best thing about it...IT'S FREE, click on the link which will take you to Inclusive Technology's website and you can get the PDF. It has loads of examples and resources which take you through the progression of switch usage and skill acquisition.
Just to add to this... http://www.inclusive.net/resources/units/unit8/unit8_contents.shtml a web page which has some detailed work on switches and switch use. Worth a look after the switch progression road map!