Some of England's poorest children are starting school still in nappies, unable to speak or to recognise their own name, according to new research.
In a number of cases, youngsters are years behind their classmates when they begin school, and can act as if they are 12 or 18 months old.
The study, by the Centre for Social Justice (CSJ) think-tank, suggests that some of England's poorest children have had such abysmal experiences in their early years that they are not ready to start learning at age five, and could be permanently disadvantaged.
The findings also show that hundreds of thousands of teenagers are leaving school each year without decent GCSEs, and that poor white boys have fallen further behind their classmates in the last five years, despite attempts to raise achievement.
The study, which examines education in England between 2007-12, argues that too many children are seeing their education suffer because of the disadvantage they face in their home life. There is "heart-breaking" evidence of youngsters trapped in severe disadvantage, the CSJ claimed.
"These children are starting school drastically behind the levels of development expected of their age," the study says. "The early years experiences endured by these children have been so abysmal that they begin compulsory schooling absolutely not ready for learning and, potentially, permanently disadvantaged."
Teachers reported that they are increasingly expected to deal with basic needs, such as potty training, and in some school teachers carry disposable gloves because pupils routinely need help going to the toilet.
Sir Robin Bosher, chair of the working group that drew up the report, said that in each class he sees, about one in 10 children are "so unsociable that they hurt others, adults and other young children" because they have had no practice at being sociable.
One headteacher told the think-tank: "In the last three years we have had to toilet train children who came to school in nappies at age five. Parents ask me how we managed to do it. Many of them just can't be bothered, they think it's our responsibility to do it for them."
The study lays blame on parents, saying that part of the problem is that they are not aware of the key developmental milestones their child should meet. As a result, teachers are spending time teaching young children "basic necessities" that they should have mastered before they started school, which cuts into teaching time.