Bale had problems with his defending when Redknapp took over last season but "the penny has dropped" with the Wales 20-year-old.
Redknapp said: "Bale was unlucky as Benoit was the improved player, he became as good as any left-back in the country. Gareth would not get in the team.
"Gareth has improved, the penny has dropped with him, there has to be two sides to his game. You see him now, he heads the ball, he makes tackles. He looks as good as any left-back there is.
"We are getting the best out of him, he has realised that he has to defend better. He is just 20 and is learning the game. His game has come on a bundle."