Agassi would have been nothing without his father. The only reason Agassi took the ball so early was because his father directed a ball machine at his feet. All Bollettieri did was annoy him so much that he wanted to turn pro to escape the academy. Agassi's book "Open" explains it all. Bollettieri had no technical input at all. He's just a guy with a lot of money to spend on advertising and accommodation. You throw enough money at the best juniors in the world and their parents send them to your academy, even if you know nothing about tennis.