I attended a Hack the Curriculum event last week in London with a number of teachers and digital industry professionals to start work on a Wikibook for KS3 Computing. It was organised by #include – a working group of Computing at School who are working to make Computing accessible for all students, regardles of gender, race, socio-economic status and special educational needs and disabilities. This will hopefully become a comprehensive resource for teachers of Computing in secondary schools, and all are welcome to edit it further.
You can access the resouce here: https://en.wikibooks.org/wiki/KS3_Computing