And the funny thing about McCarthy's work with Rodgers is I distinctly remember when McCarthy first got to Green Bay there was a lot of talk and reporting on how McCarthy and the Green Bay staff changed Rodgers' throwing motion which greatly improved his velocity and accuracy. Rodgers came from Jeff Tedford's, old school style of preloading your arm before throwing it. Anyone who played or watched high school football during the 80s and early 90s will remember how high school QBs back then would start their throwing motion with the football next to their earhole when dropping back to throw. McCarthy and staff changed this method with Aaron Rodgers. An example is discussed below:
There was plenty of reporting on this when Rodgers was backing up Farve before everyone knew how good he was going to be. Now that Rodgers has had his falling out with McCarthy it's all but forgotten.
Coach Mike McCarthy arrived in Rodgers’s second season, and he recognized the talent that spent Sundays holding clipboards. Since 1993, McCarthy has charted quarterbacks in five footwork drills that rate agility and movement. In his three backup seasons, Rodgers improved most in those areas, McCarthy said, to where he now ranks “at the top of all of them.”
In what McCarthy calls his Quarterback School, Rodgers concentrated on tuning his fine motor skills: hand-eye coordination, finger dexterity, mechanics. He also lowered where he held the ball for a smoother, more consistent motion.
By the end of Rodgers’s second year, McCarthy and Thompson saw him as a starter who happened not to start. With his quarterback coach, Tom Clements, Rodgers studied every play from the Packers’ previous season. He also took the spring practice repetitions when Favre stayed home in Mississippi.
Between Rodgers’s second and third seasons, Quarterback School consisted of 10 hours in the film room and 3 hours on the practice field a week, an offensive study conducted in “painstaking detail,” Clements said.
Eventually, Rodgers focused less on learning the Packers’ offense and more on clarifying why defenses ran certain coverages, schemes or fronts. Now, when Rodgers drops back to pass, he does not look for his receivers. He looks for defenders, where they are, where they might move, what that means or could mean. Then he throws for receivers headed toward open space.
The way he practiced behind Favre also earned Rodgers the respect of teammates. While Favre retired and unretired and eventually left for the Jets in 2008, Rodgers and Clements studied every pass Tom Brady threw in his record-setting 2007 season. Rodgers took note of how Brady “controlled the defense with his eyes” on nearly every completed pass.
https://www.nytimes.com/2011/12/03/sports/football/the-education-of-the-packers-aaron-rodgers.html