The song is from season 8 episode 1 of MLP:FiM.
♫ Lyrics for the song:
( You can support the show here: https://itunes.apple.com/us/tv-season/my-little-pony-friendship-is-magic-vol-14/id1355929287 )
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[Choir]

The School of Friendship, first day of class
Will we fail or will we pass?
Students come from far and wide
Brand-new friends here by our side

[Twilight Sparkle]

Take a breath, look around, it's amazing
I can't believe that it's real
Students galore, new ideas to explore
Can't contain the excitement I feel

Can't mess up, can't afford a mistake now
Think "success", keep it firmly in sight
Make sure to do things by the book
Make sure to do it all right

[Choir]

The School of Friendship, must get to class
Will we fail or will we pass?
Students learning from the best
Taking notes to pass the test

[Twilight Sparkle]

Wait, hold on! Not like that! Just a second!
I'm not sure if that method's approved
Let me take a look – yup, right here in the book

[Rainbow Dash]

Come on! We just got in the groove!

[Twilight Sparkle]

Can't mess up, can't afford a mistake now
We are shaping young minds to ignite
Do it like it says in the book
Now make sure you're doing it right

[Pinkie Pie]

There's not an equation on how to have fun

[Fluttershy]

The students look bored now – oh, what have I done?

[Applejack]

Can't teach bein' honest, not sure what to do

[Rarity]

I'm quite certain I'm lost

[Main cast sans Twilight Sparkle]

None of us has a clue!

[Students]

School of Friendship, another class
Wish it were more of a blast
Thought this school would be more fun
Can't wait for our classes to be done

School of Friendship




[Twilight Sparkle]

Can't mess up, can't afford a mistake now

[Pinkie Pie]

No way to have fun

[Fluttershy]

Oh, what have I done?

[Students]

Bored with this class




[Twilight Sparkle]

Think "success", keep it firmly in sight

[Students]

Wish that we could leave our desks




[Rarity]

We don't have a clue

[Students]

Listen to this one request
Make things fun, we're really stressed

[Twilight Sparkle]

Make sure to do things by the book now

[All sans Twilight Sparkle]

Can we tell her this thing is a mess?

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"My Little Pony" is owned by Hasbro,
"MLP: Friendship is Magic" is created by Lauren Faust.