Toffees boss David Moyes attracted the teen star to Merseyside after beating off competition from Tottenham, Rangers and Bayern Munich.
"He has got good potential but at the moment that's all it is," said the Everton academy director Alan Irvine.
"He has got a lot of work to do. George is a young player who was attracting interest from a number of clubs. We're happy to have him and we're looking forward to working with him here at the Academy."
Green will become a part of Everton's youth setup next summer.