“The Substitute” Debuts September 12 and Airs Weekdays at 4:30 p.m. ET/PT on MTV Santa Monica, CA (September  1, 2011)—MTV is taking over classrooms this fall with a brand new game show series, “The Substitute,” beginning  Monday, September 12 at 4:30 p.m. ET/PT. Hosted by comedian Jon Gabrus, unsuspecting students quickly find out that their…