Here are two guesses:
Guess 1: Having seen PilsNot3's guess, could it be:
GLAZED
Good luck starting this puzzle.
GL = Good Luck
You'll stop where you always do.
ZED = Last letter of the alphabet
My middle is in the ending.
A in Apocalypse
You can see on the outside that I skipped school,
GED = Alternative certification for those who skip high school
but beneath that you'll find I'm deeper.
AZ = Everything from A to Z?
Title: Stare long enough and you will have found the answer
If you stare long enough, your eyes will become glazed over.
Guess 2:
END
Good luck starting this puzzle.
You'd have to start at the end.
You'll stop where you always do.
You stop at the end, as always.
My middle is in the ending.
Actually the whole word is in "ending".
You can see on the outside that I skipped school,
ED is the notation for "unofficial drop" of a college course. For example, explained on this webpage.
but beneath that you'll find I'm deeper.
The deep end.
Stare long enough and you will have found the answer
The word "end" is in the riddle itself, in the word "ending"