Earlier this month he astonished athletics officials when he blitzed the field at the New Zealand Secondary School Championships in Timaru - winning the junior boys 100m, 200m and long jump titles.
Now he has his sights set on booking a spot in the New Zealand team at the 2017 Commonwealth Youth Games.
"We are so proud of what James has achieved on and off the track," said his dad Thomas Croft, pictured left with James.
"He has worked so hard to overcome his problems and 10 years ago we could never have imagined he would come so far with his sport.
"Constant practise and repetition has helped him a lot. When James is interested in something he will give it his all.
"We have had to get the screed redone on the back garden wall because of all the soccer balls, rugby balls and basketballs he throws around for hours every day. He has also broken a couple of the neighbours' windows with cricket balls."
James, from One Tree Hill, won his first major sprint races two years ago, running barefoot in an Auckland schools competition.
He is also a small forward for his school's premier basketball team and has been called up to the First 15 rugby development squad at St Peter's College.
"I still have trouble learning some of the training drills but other than that I seem to be doing fine with schoolwork and at sport," James said.
"The biggest problem I have is now deciding between rugby, basketball and athletics."