Dumbledore finds out about the Scoobies' mission to train the new Slayers.
Challenge:

Dumbledore offers Giles and Buffy to use Hogwarts as a safe haven to train new Slayers.

Hogwarts begins a Watcher training program as well. Required classes are a
mix of old and newly developed classes.
(This will be an extremely competetive program to get into.)

Giles is assigned Head of the Watcher department.

Dawn is in the Watcher program

Bonus:
Snape at first disagrees with the new program.

Xander eating one of those magic jelly beans
(I'm sorry I don't know what they're called) and it tastes like smelly cheese.

Xander is magicly given his eye back.

Willow is known in the Potterverse but everyone thinks she's a legend.
At least one person thinks she's joking when she says her name is Willow Rosenberg;
this person gets scared when they realize she's serious.

Andrew teaches the new Slayer History class.