House bias among Hogwarts Headmasters?

Question

Headmasters and Headmistresses of Hogwarts should be above the petty squabbling between the four houses, but are they really?

Being raised to a higher level and becoming (supposedly) neutral is a common trope both in real life and (more on-topically) in fiction. In the Wheel of Time series, "the Amyrlin Seat is of all Ajahs and of none", but except in one case, she's still raised from one Ajah or another, and sometimes retains her Ajah prejudices even though she's not supposed to. In the Night Watch series, by contrast, although Inquisitors stand above the conflict between the Watches, they are always still either Light or Dark.

So what about in Hogwarts? Snape was always shameless in his support of Slytherin, and I doubt he would have been any different as headmaster. Dumbledore arguably displayed partiality towards Gryffindor in his awarding of points at the end of book 1. What other evidence is there of Headmasters/mistresses being biased in favour of one House rather than another?

Answer 1

One example that certainly requires no speculation is Dolores Umbridge who was—nominally and, as far as day-to-day effects on students are concerned, also in practice—Headmaster for a good deal of the Order of the Phoenix.

There are many instances of her favouring Slytherin over the other houses, and in particular discriminating against Gryffindor, mainly because that’s Harry’s house. We know that Slytherin was Umbridge’s old house, so while she was never head of her house, she was favouring her own house.

Examples of favouritism include the selection of members for her Inquisitorial Squad (exclusively Slytherins if the Wikia article is to be trusted); and acts of discrimination include her ‘lifetime’ Quidditch ban of Harry and the Weasley twins after their little, hem-hem, tiff on the Quidditch pitch (even if only one of the twins was actually, erm, tiffing), while never at any point in the books (that I can recall, at least) meting out any punishment whatsoever to a single Slytherin student.

Answer 2

One example we have that does require a bit of speculation (based on other facts) deals with Phineas Nigellus (Black).

Through the interactions the various characters have with the portrait of Phineas, we see fairly quickly that he held to the sterotypical Slytherin beliefs. And though we don't know how he treated muggle-borns as Headmaster, since his family still holds him in high regard, I think it is safe to assume he didn't treat them well.

Phineas Nigellus: "Headmaster! They are camping in the Forest of Dean! The Mudblood —" Severus Snape: "Do not use that word!" (Deathly Hallows)

"You know, Minister, I disagree with Dumbledore on many counts ... but you cannot deny he's got style ..." —Phineas Nigellus's portrait to Cornelius Fudge (Order of the Phoenix)

He also was very "loyal" to his house.

"Let it be known that Slytherin did its part!" (Deathly Hallows)

He also hated teaching, and was the least popular headmaster ever

"You know, this is precisely why I loathed being a teacher! Young people are so infernally convinced that they are absolutely right about everything."

Again, we have no direct evidence (at least that I've been able to find), but these items would lead me to speculate that Phineas definately had some bias towards his old house, and probably treated them well enough while alienating himself from the other three houses.

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Now, a thought concerning the House Heads. We know Mcgonagall didn't (often) show any favoritism (excepting when she allows Harry time to practice for Quidditch to beat Slytherin, and when she distrusted Slytherins at the end of Deathly Hallows. Granted, I think the school supported her in this, so just call her the champion of the people). And we have to be told (once in the books, and once out) that the heads of Hufflepuff and Ravenclaw are Professor Sprout and Flitwick respectively. We don't see Ravenclaw getting any sort of benefit from Flitwick, and it's hard to conclude anything about Hufflepuff.