'Shocking' figures show a third of children behind at five
Almost a third of children in England are behind in their development when they start primary school, according to official figures for 2016.
And Department for Education statistics show pupils from poorer backgrounds are more likely to be lagging in their learning, literacy and numeracy levels.
The charity Save The Children called the figures "shocking".
But the government said the figures showed "a continued rise in numbers meeting the expected standards".
The Department for Education also pointed out that the gap between disadvantaged children and their peers was decreasing.
The DfE figures, published on Thursday, show 31% of under-fives were not achieving good levels of development in fields such as communication and language, maths and social skills - around 200,000 early-years children.
The figures show only 52% of children eligible for free school meals reached the expected standard, compared with 70% of all other pupils and 67% of pupils overall.
And boys lag behind girls, with 62% of boys achieving good levels compared with 77% of girls.
Detail of the figures suggests the gap between the lowest 20% of children and the average for all children has narrowed by more than five percentage points in the past four years.
But Save The Children said too many children were being denied "a fair start in life", urging the government to do more to address a severe shortfall in trained nursery teachers.
Only 654 people started training to teach early-years children this year - too few to address a shortage of 11,000 teachers for that age group, said chief executive Kevin Watkins.
"It's shocking that in this day and age so many children in England, particularly the poorest, are at greater risk of falling behind by the time they reach school because of our chronic shortage of nursery teachers, a shortage that shows little signs of improving.
"Every year, hundreds of thousands of children without access to these teachers are starting reception struggling to speak full sentences, follow basic instructions and learn subjects like maths and sciences."
Mr Watkins warned that children who are behind when starting school are "likely to stay behind throughout their lives, with huge implications for the rest of their schooling, their jobs and even their future relationships.
Liberal Democrat leader Tim Farron accused the government of "sneaking" out the statistics.
"The government have their priorities on education all wrong and are failing the least well off," said Mr Farron.
"While they pour £240m into divisive grammar schools for a select few they are leaving hundreds of thousands of children behind."
The DfE spokesman said: "We are clear that high quality early education is vital in giving all children the best chance to fulfil their potential...
"We are determined to go further to improve quality, which is why we are doing more than ever to help attract and retain the best staff and are investing a record £6bn per year in childcare by 2020."