Everton confirmed on Wednesday that the Scot will be stepping up to join Martinez's core backroom team from Monday.
Martinez said: "Duncan is developing into a really exciting coach. He has been working with the first-team on a part-time basis. He has done a really good job with the Under-18s and we feel we need his influence around the first-team on a permanent basis.
"He is an Evertonian and he is going to be a big part of the staff for the rest of this season. He brings real direction to the youngsters. When you are a young player who wants advice and direction, he is the perfect person to do that. He has also been working really hard to see the game from a different perspective to develop as a coach. He is somebody very special.
"He has got the desire and the work ethic of someone who is in love with the game. That is something that doesn't change and he can achieve as much as he wants in that area. I've seen a huge difference between the beginning of the season and now, and now is a good time for him to step up.
"Once you retire you start a new career with a new way of looking at things, from focusing on yourself to using your experience and know-how to affect and help others.
"He has been working really hard on the specifics of coaching and the way we want to play and he will be valuable in the first-team environment."
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