US Citizen, Living in Germany, Going to Xiamen

Greetings. My son (16) is an American citizen, but a student in Freiburg, at UWC Robert Bosch College. He has a NSLI-Y (US State Department) grant to study intensive Chinese in Xiamen this summer. Usually, the program collects all the passports for Chinese visas in the US, but he cannot do that, because he lives in Germany. They suggested that he get a visa directly in Germany. Does he need to visit the closest consulate (ie., Frankfurt) to get one, or can he do this by mail?

Thank you,
Andre Wakefield (dad)