MUSIC. Teachers Rock, CBS, 8 p.m. Don’t tell the kids, but it’s almost time to go back to school. To warm them up to the inevitable, try getting them to watch this new special that pays gushing homage to the U.S. educational system. In part it’s a music special taped last month with performances from the likes of Josh Groban, Dierks Bentley and Garth Brooks. More screen time is devoted to celebrities reminiscing about that special teacher that made them love learning, with taped testimonials from Meryl Streep, Usher, Jack Black, Jennifer Garner and Morgan Freeman. Viewers should also expect multiple clips from the upcoming movie Won’t Back Down, starring Viola Davis and Maggie Gyllenhaal as two determined moms trying to save their children’s rundown inner-city school.