It’s not part of the series, but the Ever Never Handbook is a GREAT add-on after the third book, before the fourth book. The artwork, the bits of information about the school and schedules, really cool! I highly recommend you read it! There are spoilers in it though, so that’s why I’d recommend it after the third book.
Picture of the school: https://schoolforgoodandevil.com/wp-c...
More Information: https://schoolforgoodandevil.com/the-...
Most Information: https://the-school-for-good-and-evil....