On an academic site listing medieval "Texts on Music in English", I found several versions of a poem called "The Chorister's Lament". It is awesome. Here it is, in all its Middle English glory. Here's an older reprint of it in a magazine, together with a nice Victorian translation at the bottom of each page.

Here's bits of it for a taster --

"Little did I know of this, when [my vows] I took --
Some notes are short, and some a long nook;
Some crook awayward like a meathook."

And here's a sample of the choir director's feedback on solfege skills --

"What hast thou done, Don Walter, since Saturday at Nones?
Thou holdest not a note, by God, in right tone!
Woe is me! Believe it, Walter, thou works all to shame.
Thou stumblest and sticks fast, as if thou were lame!
Thou 'tones not the note, any, by his name!
...Thou touchest not the notes; thou bites them asunder!
Hold up, for shame! Thou lets them all go under!"

Then is Walter so woe that well near, he will bleed;
And he wends to William and bids him well to speed.

"God knows," says William, "thereof, had I need!
Now I know why 'comes to judge' was set in the Creed!
... I have rendered nothing since men bore palms.
Is it as great a sorrow in Songs as in Psalms?"

"What? By God, you tell it! And so it is, well worse!
I solfege and sing after and I am never the nearer.
I hurl at the notes and heave them all up higher.
All that hear me ween that I err.
...
Yet there be other notes: sol and ut and la,
And that froward file that men call fa --
Often he likes me ill, and works me full woe."

There's quite a few musical notation terms I haven't heard before, in this poem, so you musician people are more likely to get those parts.

There's an Elizabethan poem by choir director John Redford that's also called "The Chorister's Lament", but it's all about spanking.