Speaking as one who teaches 6 year olds to read, and write, and draw, when they've "fallen behind" at school, I'd say starting formal schooling later would work quite well for many children, especially boys. But, there's a big but ....
The biggest influence on primary school failure is (lack of) parental language in the home. It comes from research - in the 60s! - and it's called The 30 Million Word Gap.
They found that the sheer number of words heard varied greatly along socio-economic lines. On average, children from families on welfare were provided half as much experience as children from working class families, and less than a third of the experience given to children from high-income families.
In other words, children from families on welfare heard about 616 words per hour,
while those from working class families heard around 1,251 words per hour,
and those from professional families heard roughly 2,153 words per hour.
Thus, children from better financial circumstances had far more language exposure to draw from.
What that adds up to is a 30 million word difference by the time a child is four years old.
And the content of what is said differs a great deal in different families as well.
In addition to looking at the number of words exchanged, the researchers also looked at what was being said within these conversations. What they found was that higher-income families provided their children with far more words of praise compared to children from low-income families.
Conversely, children from low-income families were found to endure far more instances of negative reinforcement compared to their peers from higher-income families.
Children from families with professional backgrounds experienced a ratio of six encouragements for every discouragement.
For children from working-class families this ratio was two encouragements to one discouragement.
Finally, children from families on welfare received on average two discouragements for every encouragement.
So we finish up with the not very remarkable notion that people in difficult circumstances and experiencing negative life experiences are much less likely to be upbeat and positive and encouraging with children.
The established connection between what a parent says and what a child learns has more severe implications than previously anticipated. Though Hart and Risley are quick to indicate that each child received no shortage of love and care, the immense differences in communication styles found along socio-economic lines are of far greater consequence than any parent could have imagined. The resulting disparities in vocabulary growth and language development are of great concern and prove the home does truly hold the key to early childhood success.
Rice University Center for Education
So that indicates that a system that starts formal schooling later could be giving the students with the biggest hill to climb an even steeper task. Because ...
Researchers found that measures of accomplishment at age three were highly indicative of performance at the ages of nine and ten on various vocabulary, language development, and reading comprehension measures.
The best education system anyone knows is (or at least was) in Finland. They start at a later age. However, they invest in the first few school years in a major, major way that no English speaking system has ever done. Basically, every sign that a student is struggling is taken as a signal to put more resources into that particular child. And if that doesn't work, they put in even more. And again, and again. So you never get a 10 year old unable to read, and then someone like me finds out they need glasses or special coaching because they can't even see the words on the page. All those issues are resolved at the first sign of any problem at all. And you never have a student move to high school unable to understand science because their vocabulary and their reading comprehension aren't up to the job.