Hogwarts students have always had the opportunity to bring animals to school, not only as pets, but also as loyal assistants and even guinea pigs for experiments.
Young wizards have brought cats, frogs, rats, owls, but now it's time to ask a serious question: what about dogs?
First of all, all the animals mentioned above are associated with witchcraft and magic in British folklore, and dogs are clearly not on the list. Also, let's not forget the Grim, a houndlike magical creature associated with death. Probably there was a superstition about dogs in the wizarding society, similar to black cats in ours.
It is also likely that all the animals mentioned in books and movies are just part of the author's vision. J.K. Rowling wanted to introduce the creatures that she believed were associated with the wizarding world, and dogs were not among them.
However, there are alternative theories. "A dog would be a bad choice for a world where everyone's most useful and cherished possession is a wooden stick," suggested one Redditor.
It would be funny if students came to class with sob stories about how their dogs stole their wands so they couldn't do their homework.
Hogwarts professors' personal preferences should also be taken into account. What if McGonagall and Filch are behind the implied "no dogs" rule? It is certainly worth thinking about.
From a rational point of view, dogs require more attention, they need to be played with, walked, and given physical exercise, and students would hardly have time to take care of their pets. Young wizards arrive at Hogwarts at the age of 11, and it would be absurd to expect them to take full responsibility for a dog that needs a lot of time and space.
Cats and some other animals can be left to themselves all day, but that won't work with dogs. As for other large pets, they are noisy and easily noticed, which can be a danger to wizards.
Owls, cats, and frogs are small and quite independent, the latter being the most important and what makes them different from dogs.
Therefore, having a dog at Hogwarts would be too much of a hassle for both students and professors. It's hard to say for sure if there is an outright ban on bringing a dog, but it would definitely not be on the list of recommended pets.
Nevertheless, the Harry Potter universe was not entirely devoid of dogs. Hagrid had Fang, and that didn't seem to be against the rules, but he wasn't a teenage student, so such a comparison is hardly fair.