Dumbledore directs the school song at the end of the start-of-term feast. His wand flicks out a ribbon that floats 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 does not appear to share Dumbledore's delight in this little ritual, but he conducts the singing with gusto and even gets a bit misty at the end of it. 

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.