"And now, before we go to bed, let us sing the school song! Everyone pick their favorite tune and off we go!"
-- Albus Dumbledore (PS7)
The Hogwarts School Song is a short anthem praising Hogwarts which is sung by the entire student body and staff on special occasions. Dumbledore directed the school song at the end of the start-of-term feast when he felt in a particularly festive mood. The last time the song was known to be sung was during the feast on September 1, 1991, when Harry Potter came to Hogwarts. Dumbledore directed the song with his wand. He flicked out a ribbon that floated in the air, creating the words for the students to sing along with, each singing to the tune of their choice. The rest of the staff did not appear to share Dumbledore’s delight in this little ritual, but he conducted the singing with gusto and even got a bit misty at the end of it (PS7).
The lyrics are as follows:
Hogwarts School Song
Hogwarts, Hogwarts, Hoggy Warty Hogwarts,
Teach us something, please,
Whether we be old and bald
Or young with scabby knees,
Our heads could do with filling
With some interesting stuff,
For now they’re bare and full of air,
Dead flies and bits of fluff,
So teach us things worth knowing,
Bring back what we’ve forgot,
Just do your best, we’ll do the rest,
And learn until our brains all rot.
The school song was not sung every year. In times of crisis, Dumbledore did not include the song in the opening festivities. With the rise of Voldemort in the mid-1990s, the song was not sung anymore (JKR).
It must be a coincidence that only Fred and George sang to a slow funeral march (PS7)!
A school song, school hymn or school anthem is the patronal song of a school. In England, this tradition is particularly strong in public schools and grammar schools (Wikipedia). It is therefore suitable for Hogwarts to have one.
The school song was omitted from the first movie (PS/f) but it was put in the fourth film (GOF/f), just before Harry, Ron, Hermione and Hagrid find Crouch sr. and a deleted scene of the fourth film, when welcoming the students from Beauxbatons and Durmstrang (GOF/f).
Also, before the interview of J.K. Rowling with Stephen Fry in 2003, the School Song was sung in the Royal Albert Hall (RAH).
From the Web
"Harry Potter: Why Goblet Of Fire Cut Hogwarts' School Song" from Screenrant
The Hogwarts School Song deleted scene from the "Goblet of Fire" film