Unfortunately, claims of children trained at one year were more due to toilet timing instead of toilet learning. The difference in toilet learning is that the toddler's brain decides he needs to go to the bathroom and the child makes a deliberate attempt to oblige. Recognizing these signs of readiness provides encouragement, not pressure. There is a great variation from child to child. Girls tend to become toilet trained earlier than boys, although early training is not a sign of intelligence.
Most children show signs of the desire to start the learning process by two years.
Children generally achieve the skill of being toilet trained between two to three and a half years. Night toilet learning may take longer for some children. It is not uncommon for children to have accidents even after they seem to be fully trained. 2001 Sioux Valley Hospital USD Medical Center.