Carrying the Flame

On the top floor of a deconsecrated Evangelical church in Berlin's Kreuzberg area, Ismet Dertli puts the finishing touches on the curriculum for a new subject being offered in the city's public schools. It's a course that hasn't previously been taught in any government-sanctioned school, at least not for a few centuries: Turkish Alevism.

This mystic brand of Islam is practiced by 25% of the more than 2.5 million Turks in Germany and up to 30% of Turkey's 66 million people — though you won't find them in any census. That's because Turkey, mindful of its fractious past,...