On Wednesday, January 14, 2015 at 12:03:10 PM UTC-5, wrote:
Piet, I don't know where you got your information, but forward slip and also boxing the wake (called "extreme Schleppfluglagen") are both required maneuvers in glider training in Switzerland.

Granted, I wasn't going for a rating there, so I didn't go through the whole training program. Maybe the instructor was just de-emphasizing the concepts.