Favors played high school basketball at South Atlanta High School, where he was ranked as one of the best high school basketball players in the class of 2009. Scout.com rated him the #1 player in the country, #2 in the ESPNU100, and #4 by Rivals.com. On March 14, 2009, he led South Atlanta to the Georgia Class AAA state championship. He scored 38 points and had 21 rebounds in the championship game against Westover High School. He was named to the 2009 McDonald's All-American Team. He led the East to a 113–110 victory and was named the MVP of the game. He scored 19 points and had 8 rebounds. Favors was selected to participate in the 2009 Nike Hoop Summit in Portland, Oregon but pulled out due to personal reasons and he was also selected to play in the 2009 Jordan Brand Classic at Madison Square Garden where he scored a game-high 21 points and was named MVP for the black team, while Renardo Sidney was named MVP for the white team. He finished his senior season averaging 28.1 points, 13.3 rebounds, 5.0 blocks, 3.0 steals and 2.0 assists per game and holds the career records in points (2,341), rebounds (1,511) and blocked shots (741).
Favors played both power forward and center for Paul Hewitt's Yellow Jackets. The front court consisted of a three man rotation of Favors, Gani Lawal and Zach Peacock. In ACC games, he averaged 11.8 points and 8.7 rebounds per game and shot 62.5% from the field. He also helped lead the Yellow Jackets to the ACC tournament finals against Duke. During the tournament, he posted 17 points, 9.8 rebounds and 3 blocks per game.
Favors was named ACC Rookie of the Year and to the ACC All-Freshman Team.