A tribute to U.S. educators features concert performances by Garth Brooks, Carrie Underwood, Dierks Bentley, fun. and Josh Groban, and recollections from entertainers, including Meryl Streep, Morgan Freeman, Viola Davis and Miranda Cosgrove. Also: a look at scenes from the 2012 drama "Won't Back Down," starring Viola Davis and Maggie Gyllenhaal.