Many children are not ready to start school when they first enter a classroom, a poll of headteachers suggests.
It suggests that many leaders believe that "school readiness" has become worse in recent years, with some claiming that more than half of new pupils are not ready to take part in lessons.
The findings come as children head back to school for the start of the new academic year.
The National Association of Head Teachers (NAHT), which co-commissioned the poll, said they want extra money for education, including the early years, as well as more investment in services for families.
Ministers have said that school funding is at its highest level, and in July, Education Secretary Justine Greening announced an extra £1.3 billion for schools over the next two years.
The poll of 780 school leaders, conducted in partnership with the Family and Childcare Trust, found that 83% of those questioned thought there was an issue with school readiness, and of these, 86% thought the issue had worsened in the last five years.
Around a quarter (24%) said that more than half of their intake was not school ready.
Asked to rank the issues causing concern, children's speech, language and communication was found to be causing greatest concern, followed by personal, social and emotional development, such as behaviour issues, and physical development.
School leaders were also asked the likely reasons why children are not school ready.
Failure to identify and support children's additional needs was the most popular answer among those that answered the question, followed by parents having less resources and pressure on family life, and then reductions in local services to support families.
Labour's early years spokeswoman Tracy Brabin said the report "should make sobering reading for Tory ministers".
"It is yet more evidence of a problem that has worsened on their watch," she said.
"It is now incumbent on the Government to ensure their spending on childcare goes towards high-quality early years education, supporting children to get the best start in life."
The chairman of the Local Government Association's Children and Young People Board, Richard Watts, said: "Investing in the early years is crucial if we are to give our children the best start in life.
"As this survey highlights, an increasing number of children are not school-ready, which is in turn impacting on their learning as well as putting further strain on school resources."
Paul Whiteman, NAHT general secretary said: "We want to see extra money for education, including early education before children start school, and renewed investment in critical services for families. Without proper investment, the youngest and most vulnerable in our society will be starting off behind, with uncertain chances of catching up."
:: The poll questioned 780 school leaders in England, Wales and Northern Ireland in June and July.