I don't know any research, but here (Australia) it's gone from perfectly acceptable to illegal in a generation. As I said, my mum has her broken wooden spoon collection (Dads belts were more durable) but my nephews aren't familiar with the concept of a spanking, let alone a belt or having your mouth washed with soap for swearing.

It was removed from government schools in the early to mid 90's and eventually made illegal in private schools too.