School readiness is one of those phrases that does a great deal of work while appearing to describe something obvious. It is used in policy documents, in nursery reports, in newspaper articles about standards, and in conversations between anxious parents. It sounds like a property of a child.
It is not. It is a description of a fit, and once you notice that, most of the confusion around it resolves.
Ready for what
Readiness is always readiness for something. A child described as not ready is not ready for a particular set of expectations: sitting for a certain period, following instructions of a certain length, managing without an adult's help in the lavatory, being separated from a familiar person for hours.
Those expectations are not derived from developmental science. They come from the way a system is organised: class sizes, staffing ratios, the age of entry, the curriculum, the assessments the school is measured by.
Change the system and readiness changes with it. A four year old who cannot manage an English reception class would be entirely typical in Finland, where formal schooling starts considerably later. The child has not changed. The demands have.
Why England asks so early
England is at the early end of the international range. Compulsory school age is the term after a child's fifth birthday, but in practice almost all children start reception in the September following their fourth birthday, meaning a substantial number begin full time education at four.
The historical reasons are administrative rather than developmental. Single annual intakes are easier to organise than staggered ones, and the current arrangement has accumulated rather than been designed.
The result is a school population in reception spanning a full year of age, which brings us to the most robust finding in this area.
The summer born effect
Within any school year group, the youngest children are almost a year younger than the oldest. In England the youngest are those born in the summer months.
Relative age effects are among the more reliably replicated findings in education research. Summer born children in England are, on average, assessed less favourably in early years, are more likely to be identified as having special educational needs, and the differences narrow with time but persist for years.
The most defensible interpretation is not that summer born children are less able. It is that a system comparing children within a year group is partly measuring age, and calling the result attainment. Where a child sits in the year is confounded with everything measured about them.
Parents in England may request that a summer born child start reception a year later, and guidance from the Department for Education covers how such requests should be handled. Decisions rest with admission authorities and outcomes vary between areas, which is a source of considerable frustration.
The definition problem
Because readiness is a relationship, definitions vary with who is doing the defining.
A reception teacher asked what readiness means tends to describe self care, separation, following instructions and getting on with other children. A policy document is more likely to emphasise communication, language and early literacy. A parent often thinks first about whether the child will be happy.
Those are different constructs, and studies purporting to measure readiness are measuring whichever one their instrument encodes. When you read a claim about how many children arrive ready, the first question is what was measured, which is the same question we ask of curiosity research in how curiosity gets measured.
Ready settings rather than ready children
A more useful reframing, and one that appears in international early years policy discussion, reverses the direction. Instead of asking whether children are ready for school, ask whether schools are ready for children.
The questions that follow are practical. Does the setting expect sustained seated attention from four year olds, when the developmental picture set out in attention in small children suggests that is a poor expectation? Is there enough adult attention for children who need help with self care? Is the transition from nursery gradual or abrupt? Is there outdoor space?
These are answerable and actionable, which readiness as a property of the child is not. A child cannot be made ready by exhortation, and a parent told their child is not ready has been handed a problem with no operation attached.
What this means for a family
Mostly it means treating the phrase with suspicion. If a setting says a child is not ready, the useful follow up is what specifically the child finds difficult and what the setting proposes to do, because that turns a verdict into a conversation.
It also means resisting the industry that has grown up around preparation. There is no good evidence that drilling a four year old on letters and numbers over the summer improves anything durable, and there is a reasonable argument that arriving with an appetite for the place matters more than arriving with a head start.
Where a specific difficulty is a genuine worry, the routes are the health visitor, the GP, and the special educational needs coordinator at the setting. Those people can see the child.
The underlying point
Readiness talk locates a systemic design decision inside individual children. England starts school early. That is a choice, defensible or not, and one consequence is that a proportion of four year olds find the demands hard, which is what you would expect and not a discovery about them.
Understanding the phrase as a description of fit does not change the timetable. It does change who is being described, which is worth something when the description is of your child.
For how the year itself works, see the reception year in England, and for how differently the rest of the United Kingdom does it, four nations, four systems.