Being parents is tough. Maybe your kid is just unmotivated. Instead of spanking, I think it's important to improve on communication through common hobbies. Teenagers in Germany need to learn a lot of survival and self-sufficiency skills such as hiking, hunting for food, build campfire for cooking, pitch a tent, emergency CPR, first aid and etc. Sometimes, kids are unmotivated because they only see a dead end to their hard work. They see their parents studying a lot and yet still struggle in life.