Besides, it's not like he had anything to do on the platform. His mother had suggested taking off work to see him off, but logically it was no different saying goodbye on the platform or saying goodbye before he got in the taxi, so he didn't want her to have to go out of her way. King's Cross was about 30 minutes away from where they lived, and in the opposite direction of her work. He'd hugged her goodbye when he left in the morning, and promised to write as soon as he got to school, so there was no waving, no final farewells, to make him linger on the train station platform.
There were many empty compartments when he got, but he walked a little bit from the door to pick one further down along the train. Sitting by the window, he'd already put his small bag up on the luggage rack above him. Several books were stacked on the seat beside him to read during the trip, just in case no one did end up joining him. He was excited, and a little anxious, about the coming school year though. Talking to someone who was going through the same thing, or someone who had been through it previously, seemed like just the thing to work off some of that nervous energy. So he was sort of hoping someone would come and sit in there.