Weighing in at a massive 140kg, Walker lost 2kg to compete at the nationals in Tauranga and went into the final of the 81kg+ grade at 138kg. He was fighting Auckland-based nationally ranked under-90kg brown belt Grayson Thomas, who is in the New Zealand training squad.
"He beat me and I got silver, but when it came to the final of the open grade junior men bout I turned the tables and beat him. I realised I had taken him too lightly in the first fight," Walker said.
In the beginning Walker used his weight advantage to close his opponents down, but is now leaning much more to technique to achieve his goals on the mat.
City College Judo Club coach Garry Davies said his development in such a short time was unusual and predicted the youngster had the potential to represent New Zealand in the future.
"Sione has a lot of raw talent, but has plenty of potential and is on a pathway to representing his country at some point. Sione is currently ranked No3 in the country in his age division, which relates to the 100kg+ grade," Davies said.
"He did tend to use brawn rather than technique in the beginning and even now he tends to be quite gentle with his opponents because of his size. These days, halfway through a bout, he'll realise that he can use both strength and technique to get the job done."
Martial arts, including judo, not only teach fighting techniques, but also self-discipline, self-awareness and respect - values Walker has embraced over the past 15 months.
"Sione was not on a good path before taking up judo. Nothing overly bad, just doing his own thing despite what he was being asked to do by teachers and that included a bit of truanting. Judo has given him focus and that is beginning to pay dividends in life and in the sport. Sione is far more settled in himself and has a far better attitude and more respect for himself and others," Davies said.
The focus now for Walker is the North Island championships at the end of August in Gisborne and the nationals in Wellington at Labour Weekend.
Meanwhile, fellow City College club members also had success in Tauranga. Antione Rahier won bronze in the under-60kg division and Finn Brown won bronze in the lightweight open.
Wanganui Judo Club's Aiden Voice also won bronze in the under-90kg and open divisions.