Malkin Academy: The Cup of Kings

"Could the oldest wizarding school in America hide a weapon that would have made Voldemort unbeatable? The daughter of the young wizard who almost solved the mystery needs to know—before the answer destroys her family! A celebration of American wizardry."

A novel-length fanfiction by one Dr. Platypus. The story came about thanks to the author's daughter wishing she could be a witch, and being a pretty good writer, he decided to do something about it.

Jessica is 11 years old, starting her first year at the titular Malkin Academy, the premier Wizarding School in America. She meets Kate, whose father becomes wrapped up in a mysterious plot going all the way back to earlier days of the academy. As he's hauled off by guards, Kate and her friends must solve the mystery behind the Cup of Kings while Jessica attempts to carve her mark into the brand new world she's joined. A colorful cast of down-to-earth, relatable original characters and a setting rivaling JK's own abound.

Tropes present in The Cup of Kings:

 * Dark and Troubled Past: Kate's father. The mystery starts out by hinting at one of these.
 * Wizarding School: Malkin Academy. It's basically the heart of American Wizard schooling.