Savannah I agree with Jordyn. The Hex Hall trilogy is fantastic. I could barely put it down, which is something that hasn't really happened since Harry Potter. You should definately read the Hex Hall trilogy. As Jordyn said, you won't regret it.
Rachael No, they mention the main character(s) from Hex Hall though, so there maybe a tad of a spoiler. I highly suggest reading the Hex Hall trilogy before starting School Spirits. Not because you'll be out of the loop if you don't, but because it is a really good trilogy and you'll want to read it after finishing this book anyway, so may as well start with the series that's complete. ;)
Day Nie I had read Hex Hall trilogy this year, and I read it on stride until finish the 3rd book..haha