To this perennial novice, this is a reassuring thread. I've felt very sorry for my teachers, who play so beautifully -- and then they had to listen to me rattling the strings for a half or 45. Here's a little waltz in G I found, titled Cead Mile Failte, that says it's "dedicated to a teacher of music" and by implication seems to be dedicated to all music teachers.
1. Oh, wizard I beg hear my plea, won't you sing me a map to the key,
that can un-lock a heart, near to bursting apart,
with music that yearns to be free, with music that yearns to be free.
2. He said go where the mute swans do sing,
Go where Scylla wears blue in the spring,
Swing your case, full of hope, up a challenging slope,
Twist the dragon's tail and he rings.
Cho: Cead mile failte, cead mile failte, go where your need will be welcome, Cead mile failte,
Cead mile failte, a hun-dred thousand times welcome.
3. Find a link to the great green neck-lace,
Cross where old Muddy River once raced,
Hear elegant fingers delight silver strings,
Where these words mark a magical place, where these words (etc.)
4. Comes a day when your lessons are o'er,
Though, apprentice, you must learn much more,
Make a friend out of time, Gentle touch sounds the chime,
Let these words from an unlocked heart pour.
2nd chorus: Go raibh maith aggot,
Go raibh maith aggot,
May much good be upon you,
Go raibh cead mile maith aggot, Go raibh cead mile maith aggot,
A hundred thousand times, thank you. A hundred thousand times, thank you.
(line breaks added by a Joe Clone)