"To make the cut you've got to be making finals, and he just didn't seem to put it together in the events this year," Ruddell said of Scott-Arrieta, who was named as a non-travelling reserve.
"Within the competition setting there are so many variables as to who will do well and who won't [for example the conditions]. Just on a couple of events he got unlucky, a couple he surfed well but others surfed better.
"He's just going to have to turn up next year with a really good attitude and get a couple of results and he'll make the team.
"He's got the ability, there's no doubt about that, he's been picked for a long time, but like I said, if you're not making finals it's hard to make the team. You see that in the surfing world, you see a lot of people who aren't the best on the board but they know how to win."
The World Junior Surfing Championships are an annual event, having been held since 2003. New Zealand have competed at the event since its inception and have been placed 10th at the 2012 event in Panama. The competition begins on June 8 and runs until June 16.