Beckham's performances against Estonia on Wednesday and last week against Brazil have led to claims that he should not have been left out by McClaren in the first place.
But the England manager insists he made the right move after the World Cup - and also did the same when he decided to bring the Real Madrid player back into the international fold.
McClaren said: "I wouldn't change the decision [to leave him out], I felt it was correct at the time for everybody, the squad and the team.
"I wouldn't change my decision to bring him back either. I felt it was the right time, and if he had been fit for Andorra and Israel it might have been earlier - in October he wasn't in the Real Madrid side.
"I just know that what we are seeing now is David Beckham the player that everybody knows."
McClaren said he has not been surprised by the way Beckham has reacted to his original omission from the former Middlesbrough manager's first squad last August.
Asked why it had taken a shock to the system for Beckham to respond, McClaren said: "Believe you me it doesn't matter whether you have the best talent in the world or the lowest talent in the world, in all walks of life, in business or in sport, it just becomes more evident and more plain in sport.
"It has taken a shock, both individually and as a team, to change things and that is what has happened.
"You come across adversity and it's how you react - for example Michael Owen has reacted to his injury by coming back better.
"It's the in-born character and we need people like Michael and David, those type of characters.
"David has reacted exactly as I thought he would when that decision was made, he's taken a conscious effort and since the new year he has looked fitter, stronger.
"He knows what to do to maintain that standard.
"I always said what kind of reaction would you expect from David Beckham - exactly what we got. He's gone away and come back better, fitter and stronger, certainly the last two performances he has been excellent."