Why we cap classes at eighteen

Every independent school will tell you its classes are small. Fewer will tell you exactly what that means, why it costs what it costs, or what a teacher can genuinely do differently when there are eighteen children in a room rather than thirty. This post tries to answer those questions plainly.

The number is not arbitrary

Eighteen is not a round number chosen for the brochure. It sits at the upper edge of what research into working memory and classroom attention consistently finds manageable for one adult. A teacher moving around a room can hold roughly fifteen to twenty children in active awareness — knowing who has gone quiet, who is rushing, who reached for the rubber three times in five minutes. Beyond that threshold, children start to become faces rather than learners. Thirty is not twice as hard as fifteen; in practice it is considerably more than that, because the complexity of relationships and individual needs does not scale linearly.

What a teacher can actually do

The differences are concrete, not philosophical.

Hearing every child read

In the early years, reading aloud to a teacher one-to-one is how children learn to decode. In a class of thirty, a teacher who spends three minutes per child uses up the entire teaching day on reading alone, leaving nothing for everything else. In a class of eighteen, a teacher can hear every child read individually at least twice a week and still have time for phonics work, writing, and mathematics. That is not a small difference in a child's first years of literacy.

Catching a misunderstanding inside the lesson

When a child misunderstands how to carry a digit, or reads a question about fractions the wrong way, the moment that matters is during the lesson, not at the end of term when a test reveals it. In a smaller room, a teacher circulating during independent work will reach every child two or three times in a single session. A misunderstanding corrected on a Tuesday morning does not become a gap that sits quietly for six weeks and then compounds.

In a class of thirty, a conscientious teacher circulating will reach perhaps eight to ten children in the same period. The others receive feedback on their books three days later, after the lesson has moved on.

Writing in the margin rather than assigning a grade

Marking thirty books in a way that is genuinely useful — a specific question, a pointed observation, a suggestion that goes beyond ticking — takes around four hours. At that volume, marking becomes a system of grades and brief codes because there is no time for more. Marking eighteen books carefully takes around two hours. That is still a significant demand on a teacher's evening, but it leaves room for the kind of feedback that tells a child why their argument did not land, or what their next draft should actually do differently. A grade on its own rarely changes anything.

What this costs, and why fees are what they are

Small classes are expensive. It is worth being direct about this because it is the main reason fees at independent schools are substantially higher than the cost of state provision, and parents deserve to understand what they are paying for rather than being offered vague talk of "ethos" and "community".

Teacher salaries account for the largest share of any school's budget — typically around sixty to seventy per cent. A school running classes of eighteen needs roughly two thirds more teachers per hundred pupils than one running classes of thirty. Those teachers need classrooms, which means more space per pupil. More space costs more to heat, clean, and maintain. None of this is waste; all of it is structure that directly determines what happens in lessons.

There are other costs — specialist teachers for art, music, languages, and physical education; learning support for children who need additional time or a different approach; the administration that makes a school function day to day. But the class size itself is the structural decision that sets the floor. Everything else is built on top of it.

A note on what small classes do not fix

A small class with a weak teacher is still a room with a weak teacher. Class size is a condition, not a guarantee. What it does is remove the structural barriers that prevent a skilled teacher from doing the things they were trained to do. It also removes the pressure that drives experienced teachers out of the profession — the sense that no matter how hard they work, they cannot adequately serve thirty children alone. Retention matters. A school that keeps good teachers for ten or fifteen years holds institutional knowledge about how children learn that cannot be replicated by a staff that turns over every two years.

If you are weighing up whether the fees make sense for your family, the honest answer is that the calculation is genuinely difficult and only you can make it. What we can tell you is that the money is not going towards grounds, branding, or facilities that photograph well. It is going towards the ratio of adults to children in rooms, and the time those adults have to know each child's work. That is where learning actually happens.