Dennis is extremely excited to be starting at Hogwarts, and joins the rest of the first-years on the boats to the castle. When the first-years enter the Great Hall, Dennis is draped in Hagrid's large moleskin overcoat; the coat is so big for him it looks as though he is wearing a furry black marquee. After he has lined up with his peers, he catches his brothers eye; he gives a double thumbs-up and mouths that he fell in the lake on his way to the castle, looking positively delighted about it. Dennis is sorted into Gryffindor, much to his brother's relief.
Dennis waits outside the castle for the Beauxbatons and Durmstrang delegates to arrive with the rest of the students. Dennis's suggestion that the Beauxbaton's students are arriving in a flying house is the closest anyone gets to identifying the horse-drawn carriage.