Nope, not scary here. Can't wait for him to get away from his fairly clue-less primary to the secondary which I know has an excellent pastoral record, stimulating teaching and a warm and welcoming atmosphere. Size isn't everything- and it's definitely not the same for an almost-teen as it is for a smaller child.
My little lad was waaay less perturbed about Big School than I was! He's small, not particularly street wise and just above average academically.
Now, here at the end of Y7, I can say so far, so good. The schools had done an excellent job in preparing the pupils and he was good'n'ready, even if I wasn't! (Again, into a year group of 280). Really, most have outgrown Primary by the end of Y6, and those who aren't quite ready have already been identified by your primary to the secondary and Steps Will Be Taken.
My DS1 who was so slow he couldn't catch a cold previously has managed to not miss the bus once this year and the sanctions for not-done homework (which are always bigged up to the DCs!) have ensured the homework 'battle' is between him and the school, not so much me any more. Halleluja!