knowledge
Harry Potter grew up knowing he was being watched. He knew it the way he knew he was eleven years old - the knowledge impacted his every action and, more importantly, his every interaction. From the neighbors and teachers to the Santa Claus impersonators at the mall, Harry never had a single moment, a single interaction, without the assumption or knowledge that it was being observed by his aunt. Whenever he forgot, in the few minutes he would pretend to be a normal child, one allowed to have secrets, his aunt would find out, and he would be punished for daring to forget his place, daring to pretend that a freak like himself deserved a shred of privacy. Harry Potter was not to be trusted.
In many ways, Harry's childhood on Privet Drive prepared him well for his first experience in the Wizarding World. The worst part of suddenly being famous, after all, was the loss of privacy. Harry never had that, and therefore he never knew the difference between his former infamous reputation and his new famous one. Either way, he was being talked about by the other kids. Either way, he wasn't normal.
"Our newest celebrity" the Potions Master sneered, and the tone was that of a thousand other adults Harry had introduced himself to, the tone of "of course, you're the little Potter boy. You're the newest troublemaker."
"Yessir, I'm here." And Harry stuttered out his lack of knowledge about Potions, recommended the Professor call on somebody else, and the idiocy hurt, the way it always hurt, but Harry was not embarrassed. Embarrassment only occurs when you had any dignity to begin with. The difference between James Potter and Harry James Potter, other than that they wore different ties, was that Snape could hurt James Potter because James Potter had been arrogant. The Potions Professor could not hurt Harry because Harry didn't care about what his classmates thought, or what he deserved. Harry never angered the way James had, the way any normal child would have. He took the mistreatment like he had been treated this way his entire life, because he had, and that infuriated Snape more than a million sarcastic remarks would have.
If Severus Snape cared about his students, he would have seen Harry's casual acceptance for what it was. As Severus Snape was, he saw the boy as his childhood nemesis with a new form of torture under his belt, and the Gryffindors were to pay for it. Neville Longbottom left most classes in tears, if he wasn't in the hospital wing.
As for Harry's other classes, Harry loved them. He sat up front in Transfiguration, with a closeup view for Professor McGonagall's Animagi transformation from cat to person again. Harry Potter made a nice impression on both Professor McGonagall and Professor Sprout, the only thing of concern being that he never looked at their faces.
Harry's favorite class, however, was History of Magic. He watched the ghost with bright eyes, taking detailed notes not only on what the Professor said, but also what he called them. Harry was determined to find out what time the man died, and why he stayed at Hogwarts rather than move on. Did Binns notice he was disliked by most of the students? If so, why did he act like he didn't? If he did, why continue? Harry knew that if he had had any way to go from being hated to being liked, he certainly would have done whatever he could do to be liked.
Harry didn't have to worry about being disliked anymore, not now at Hogwarts. His classmates all talked to him, which was more than any interaction he ever had beforehand. Harry didn't realize, by the end of that first day, most of the other kids have already become close to one another. He didn't realize, as he took detailed notes on the length of Binn's pauses as well as the House Elf Rebellion for Michael Corner, the rest of the grade was making friends.
Harry Potter was used to being watched, so he didn't notice that most of his interactions with the other students were only their watching him and whispering, rather than genuine attempts to get to know him. Harry didn't realize that he still had yet to experience friendship.