Italy Under-20s failed to win a game in 2012 RBS 6 Nations but pushed their Welsh and Scottish counter-parts close in their final two games before losing 30-23 and 20-17 respectively.
Green, who won the 1987 World Cup as a player with New Zealand, also headed up Italy's academy in Tirreno after being appointed to the role in 2010 and insists he'll be sad to depart.
"I thought I had started some good work. In the Six Nations we made errors, I made errors but we were starting to see something," he said.
"There was growth, a project, we started to see a game.
"All of that in a few months of work and I ask myself 'what could have become of that squad if that group of boys had a whole season to work together?'
"I can calmly I say I still have something to give."