Firstly congrats on your son getting into Trinity. I've heard its a very good school and a tough entrance exam. I know a boy who started Year 6 last year at Trinity and lives in the area. He's done a similar commute by himself since he started. If the Japanese can send their 3yo's on shopping runs alone, then your boy should be able to catch a bus and a train. Get him a phone, either a smart one if you want to track him or a Nokia brick so he can make calls if there's a problem. After a week or two, he'll be fine with it. Best of luck.