Ground-breaking research by one of Scotland's leading educational psychologists suggests that boys who start school aged four-and-a-half are at a disadvantage - and that it stays with them until they finish secondary as Christmas leavers.
Alan McLean, who works for Glasgow City Council and has focused on pupil motivation, argues that many immature boys never catch up with their peer group. Mr McLean argues that the chronic stress of facing social and educational barriers has a long-term effect on the development of their personalities and ultimate life chances.
On the basis of his survey of 1,400 primary 6 children across 50 schools in Glasgow and 1,000 teachers, he is calling for the debate on school entry to be reopened. The current structure is, he says, "a monolithic one-chance system" which needs to be more responsive to different needs.
One of his more radical suggestions is that because of the proven gender gap, girls should start at the age of five and boys at the age of six. He acknowledges that such a proposal would have political and social sensitivities.
Another suggestion is that children should have a staggered start to school, only entering once they reach the age of five.
While acknowledging the success of nurture classes for P1 and P2 children, which he points out have a disproportionate number of younger boys in them, he is calling for a more sophisticated, multifaceted approach to tackle the disadvantage younger boys face.
His analysis of the impact of starting ages at school comes from his wider work on the SELF project (Social Emotional Learning Framework), which is being carried out in Glasgow and partially funded by the Scottish Executive.
It is aimed at creating an in-depth, almost clinical, assessment tool of children's ability to engage in learning, which could have a number of applications - from helping primary-secondary liaison to establishing whether some children would be better suited to a special school environment.
Part of Mr McLean's work on SELF involved 1,000 teachers giving their perceptions of the children they teach, which led him to create a 16-dimensional "engageability index". He used this to analyse 1,400 P6 pupils - an age chosen because he believes that this is the stage when many of the future NEET group (not in education, employment or training) turn their backs on learning.
Scoring the P6 pupils from 0-10 across his 16 dimensions, he analysed the results for engageability according to gender and date of birth. That produced scores of 7.6 (older girls), 7.3 (younger girls), 7.0 (older boys) and 6.6 (younger boys). Another test of learning competence (which looked at attention, focus and other factors) showed older girls had a score of 7.4, younger girls 7.0, older boys 6.8 and younger boys 6.4.
On engagement and motivation, older girls scored 7.7 and younger boys 6.4.
And when the children were given a sophisticated reading comprehension test - a proxy test for ability - the top group of above average older girls scored 8.0 compared to the below average younger boys' score of 6.3.
"The notion of mixed ability tends to be limited to ability but, if you take in motivation, the groups are on different planets," Mr McLean said.
"It's quite scary."
One of his concerns is that when teachers are making sense of a class they tend not to know how old each child is. "But it's a very important variable, and it's particularly important when combined with gender," he said. "I would have thought the differences would have washed out by P6 but they have not at all."
He also fears that some primary teachers may be mistaking immaturity for inability.
Even if reforming the entry system is not possible, he would like to see a greater development of learning through play in the early years.
"Five-year-old boys are built to play - they are like dogs," he says. "Putting them in a seat and asking them to sit all day is incompatible with their brains.
"There is too great an emphasis on the formal structure of learning in P1.
It's making demands on the psychology of five-year-old boys - for all four-and-a-half year-old boys it's a step too far."
Danny McCafferty, head of Fasque Family Centre in Glasgow and a former education spokesman for the local authorities, said his 25 years'
experience in pre-five and primary education backed up Mr McLean's findings.
"You have got to get young children emotionally ready to cope with the emotional rigours` of school," Mr McCafferty said.
Research commissioned by the Scottish Executive, published last summer, found girls to be slightly ahead of boys in early reading, phonics and vocabulary, but not in maths.
It added: "A year's growth around the age of five has a marked impact on a child's cognitive development, and it is not surprising that we found this had a clear link to age."
The study, however, did not find that younger or older children did unusually well in terms of educational progress. Nor did it find any connection between the age of the child and the attitude of the child in the year group.
The research team from Durham and Dundee universities concluded, therefore, that there was no evidence for an optimum age to start school.