Two-year-olds from disadvantaged families should be enrolled in school nurseries to improve their chances, the chairwoman of Ofsted has suggested.
Many children from poor backgrounds have a "dire" start to their education, according to Baroness Sally Morgan.
They can be up to a year and a half behind their better-off classmates by the age of five, she said.
The Pre-School Learning Alliance described Lady Morgan's suggestion as "beyond belief".
"Who would disagree with Sally Morgan that children from disadvantaged backgrounds need considerably more support. However, to suggest that placing two and three-year-olds in schools is the answer is beyond belief.
"Social inequality needs to addressed in many ways and taking very young children away from their parents and placing them in formal schooling is not the answer," said Alliance chief executive Neil Leitch.
Mr Leitch added that international research put the UK's specialist early years network of childminders and nurseries among the world's best.
"I am struggling to understand why anyone would promote pushing our youngest, most vulnerable children into schools rather than using the existing network of specialist local provision offered by childminders and group settings," he said.
The government said it was making it easier for schools to take children from the age of two.
Speaking at an event organised by an academy chain, Lady Morgan argued that poor parenting, poor diet and poor housing meant disadvantaged children were often not ready to start formal schooling at five.
She called for a "big brave move" in early years education, with more nurseries attached to schools and a particular focus on the poorest children.
She said more schools should become "all through", taking pupils from age three or younger to age 18.
Her comments echo a recent Ofsted report which suggested that poor five-year-olds are 19 months behind their more affluent peers.
"What a dire start to their educational life," said Lady Morgan.
"Those children had low level social skills especially reading and communication.
"They're not ready to learn at school. Weak parenting, low educational attainment of parents, poor diet, poor housing and so on.
"The gap between affluent and disadvantaged is greatest in that group.
"No-one has yet got a grip on this problem", she said.
"I think there needs to be a big brave move on the under-fives agenda to target funding heavily on the children who will benefit most and increasingly, I think, to look to strong providers to go further down the system. We've increasingly got five-to-18 schools, why not three-to-18?"
A Department for Education spokeswoman responded: "We know that teacher-led early years education has a positive impact on children, especially on those from low income backgrounds.
"That is why we are making it easier for schools to take children from the age of two by removing the requirement on them to register separately with Ofsted when doing so, and introducing 15 hours of free early education for 240,000 of the poorest two-year-olds."
The spokeswoman said government reforms would ensure all children, regardless of background, get a good start in life with all three- and four-year-olds entitled to 15 hours a week of free early education.
Educational Psychologist Dr Jo van Herwegen of Kingston University said formal learning risked damaging children's development if started too early.
"It's really all about what you define as being 'school' education and the government needs to understand that children learn through play at this young age.
"Formal learning is extremely difficult as children's working memory and language abilities are still developing,
"Forcing children to learn in formal settings and sit tests regularly can risk creating performance anxiety and an aversion to learning later on in life".
Wendy Ellyat of the Save Childhood Movement said the key was to "prioritise child-flourishing and well-being over educational attainment", whether children were with childminders or in schools or nurseries.
"We also need to look at how best to support parents as the most important thing for such young children is to have stable, loving and supportive home lives."