For the anime fans, in the early settings of the Natsume Yuujinchou, since Kitamoto always seems to hang out with Nishimura, the animator probably thinks that they are classmates. Two best friends usually from the same class right? There are some scenes when Kitamoto shown sitting behind Natsume in class, or is that after school hangout time?
Anyway, later on, it was shown that Kitamoto actually in another class, 2-5 together with Tanuma, the new transfer kid. Only much later, we see that Kitamoto and Nishimura are NOT classmates. But it true, they've been best friends since childhood. I think the animator not to be blame for this peculiarities, even in the manga, Kitamoto's class have not been said in the first place. Or maybe, Midorikawa wanted for each of the new transfer students (Natsume & Tanuma) to have a best friend in each of their classes? One for Taki too then :)