Have you already checked out Education.com's Homeschool information center? http://www.education.com/topic/homeschool-overview/
 
There is a lot of information there that you may find helpful, including a section of articles about "Homeschool and the Teen Years."
http://www.education.com/topic/homeschool-teenagers/
 
Additional resources you might also review...
 
Preteen Years (9-13)
http://www.education.com/age/preteen-years/
 
Teen Years (13-19)
http://www.education.com/age/teen-years/
 
The Parent's Guide to Middle School
http://www.education.com/grade/middle-school/
 
There are also activities on Education.com that are specific to middle school children here: http://www.education.com/activity/middle-school/