It has come to my attention that Hogwarts needs an English grammar class. So I will provide

YOUR = indicating ownership of something
"That is not your telescope, please give it back."

YOU'RE = a contraction (combination) of you and are
"Students, you're going to have to point your telescopes at the sky instead of the girls' dormitory."

THEIR = a possessive pronoun.
"Their handwriting is illegible."

THERE = adverb meaning 'that location.'
"Do not stick your wand up there!"

THEY'RE = a contraction of 'they are'
"They're going to lose more than five points if they don't stop pestering Mrs. Norris!"

I AM JUST GETTING SO MAD WRITING THIS HOW AM I SUPPOSED TO TEACH CHILDREN

SHOULD'VE = a contraction of 'should have' NOT SHOULD OF THESE KIDS
"I should've done my homework last night instead of eating doxy eggs."

ALOT = A LOT

There will probably be more added to this list as the school year progresses.