TWOP has been discussing blanket training lately. My mom didn't do it with me or my older siblings but she did it with my younger siblings. I remember Luke and Matt having an especially rough time of it. In my house, it worked the way I'm about to describe it but this varies household-to-household. I think it probably depends on how quick the parents are to adopt the "spare the rod" ethic.
Matt and Luke were placed on their own blankets. One thing people don't hear is that those blankets aren't big. They're not supposed to be bigger than a bath towel or crib quilt. Each child had their own to reduce the temptation to play together. I was told that playing together during blanket time wouldn't encourage self control and I never understood that because that's when we exercise the most self-control (in dealing with others, right?). If the boys went off the blanket, they were slapped on the hands or feet. Whatever body part went off first. If they cried they had to sit for added minutes on the blanket. My mom started when the kids were starting to crawl so ages depended on how mobile the child was. Matt was very mobile so he got the worst in blanket training. We also weren't supposed to talk to the child who was in training.
What is worse than the child's experience is the mother has to deny impulses that I think come naturally. If the child cries to be comforted during training time there's no out to pick him up because "you're giving in" to the child's lack of self control. Moms turn off the natural instinct which leads to more problems and disconnects between mother and child. It also encourages leaving your child alone more often than not. I can't explain how but it does. I've seen moms forget about the baby on the blanket.