Most children in England are entering school aged four, a year younger than the official starting age, because of pressures on funding and getting good test results.
The TES found that most councils surveyed have moved to a September start for all pupils. The change means children born in August begin school just weeks after their fourth birthday. Parents are complying because they fear they will not get their child into the school of their choice.
Since 2000, the curriculum for four-year-olds has been the same whether they are in reception, nursery or private day nursery. But Lesley Staggs, an early childhood consultant, said: "What bothers me is that the staffing ratio for reception classes is one adult to 30 children. There is a good reason why we have always gone for a ratio of one adult to 13 three or four-year-olds in nursery classes. At that age children are developing their language and social skills."
Those in favour of a September start argue that the longer children are in school, the more successful they will be. Teachers and heads say children are better prepared for Year 1 if they enrol in reception from September.
And inspectors believe schools do better if children have a full year in reception.
But early years experts fear that putting such young children, especially boys, into school does not raise standards. A study of 1,400 children in Glasgow, published last year, found that boys who started school aged 412 were at a disadvantage, which stayed with them until they left secondary school.
The TES survey of 66 local authorities shows that in more than than half, all children start at the beginning of the school year in which they turn five. Fewer than one in 10 still have an April starting point, compared with more than one-quarter in 1997. One-third have two starting points, September and January, compared with 24 per cent in 1997.
Four authorities are switching to a September-only start from 2008, and two others are also considering a change. If the trend continues, in the next few years 68 per cent will have a September-only start, one-quarter will retain January intakes, and a handful will admit in April.
In Wales, seven of the authorities that replied have had a September-only starting point for more than 10 years.
School funding is based on the number of pupils on the census day in January. This creates an incentive to have all reception-year children in class by then.
Although parents are not required by law to send their child to school until the term after they turn five, in practice few will hold back their child if all their classmates begin in September.
Lynda Barrett, head at St Ann's Well nursery and infant in Nottingham, said: "Under a three-point admission system, children whose birthdays are in the summer miss out on so much. Our children do a whole reception year irrespective of when their birthday is."
Liz Steele, head of Glemsford primary, Suffolk, said: "There is no doubt about it, those children who start in April are not so ready to go up to Year 1. We have at times kept them down for another term, then moved them after Christmas, but that has disadvantages because they see the other children go up."
Is four too young? page 15 Leading article, page 26