There once existed a real Witcher school in Poland. I say "once" because the school had its license pulled by CD Projekt Red back in February. The reason for the license getting pulled may be due to one of the school's staff belonging to a prominent alt-right group.
The Witcher school in question was named 5 Żywiołów, or 5 Elements. It began in 2015 and held roughly 40 events over seven years...