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Just in case anyone else has trouble finding it and sees this:

After leaving the school, walk straight down to the trees and to the right and you'll run into a small opening, follow the XP dots and you'll run into a bit of a forest maze bit, go to the center block area with a ghost inside it and wrap around it to continue following the path out of the forest.  (Don't go to far to the left near the ghost box, there is a really powerful wisp there.)