Part 2 made the strongest case I could for nursery, and I meant all of it.

But there is research pointing the other way. Some of it is very solid. Some of it is weaker than people claim. And one popular argument against nursery has actually been disproved, which I will come to.

Here are four things.

First: a day at nursery is physically harder on a toddler than a day at home.

Our bodies produce a hormone called cortisol. It rises when we are under pressure. Normally it is high in the morning and falls slowly through the day.

Researchers measured it in the same children, at home and at nursery. At home it fell as expected. At nursery it often rose instead.

Be careful with this finding. Cortisol also rises when a child runs, gets excited or does something new. No study has shown that this daily rise causes long-term harm.

Why this is a point for home: whatever a nursery day asks of a small child, home asks less. If both options are decent, one of them is easier on his body.

Second: the first weeks are hard for him.

One study followed children at fifteen months, close to my son’s age. It measured them at home, then while their mothers stayed with them at nursery, then after the mothers began leaving. In the first hour after the mother left, their cortisol nearly doubled.

There is a second half to this. Another study followed children for three months. The early weeks were hard. By the third month the levels were normal again, and both parents and staff said the children were doing well.

Why this is a point for home: starting nursery has a real cost, and the child pays all of it. Staying home has no such cost. Most children recover, but you should know you are asking him to pay something.

Third: at home, nobody else is using the adult.

This is the biggest point, and several others come out of it.

To be fair, a nursery room is usually not one adult alone. Many have a teacher plus two or three helpers for around fifteen children. That is a reasonable amount of adult attention.

But it is shared attention, and shared attention is not the same as attention that belongs to one child. Four things follow from that.

He waits. One child falls, one cries, one needs changing, one is hungry. The adults have to choose an order. At home there is no order, because there is nobody else in the queue. That immediate response is one of the main ways very young children learn.

He may hear less language, not more. This surprised me, because language was the strongest argument in Part 2. One study recorded children’s whole days and counted the words adults said, the sounds the child made, and the exchanges between them. The children got more of all three at home. The reason is simple. A toddler points at a bird. The adult says “bird.” He makes a sound. She says “yes, it is flying.” He points again. That conversation can continue because nobody else needs her.

Nobody knows him as well. A person who looks after the same child every day learns a great deal. That sound means tired. That cry means hurt. That gesture means water. This song calms him. Children can form real relationships with nursery staff, as I said in Part 2, but knowing one child that well is harder when you are responsible for fifteen.

He loses control of his own day. A toddler gets tired at unpredictable times. He eats badly one morning and is hungry by ten. At home, someone can simply react. Fifteen children need a schedule. Meals at a set time, naps in a system.

Why this is a point for home: at home the day is built around one child. At nursery the child fits into a day built for fifteen. The staffing may be perfectly good, and it is still not the same as having someone to himself.

Fourth: he will get sick more. This one is not in dispute.

A Danish study followed more than one million children. Starting nursery caused a clear rise in infections, and the rise was larger the younger the child was when they started.

And the extra illness was not repaid later. The common idea that they get sick now so they get sick less at school did not appear in the data.

Why this is a point for home: this is the only cost on either side that is certain. Nursery means more illness, for him and for the rest of the house, and nothing later cancels it out.

And one argument that is weaker than people think

This is the one you hear most often, so it needs care.

The large American study found that children who spent more total hours in childcare over their first four and a half years showed more difficult behaviour later. More aggression, more conflict with adults.

If I wanted to make a dishonest case against nursery, I would stop there.

But newer research combined data on more than ten thousand children across seven studies in five countries. Instead of comparing different children with each other, they checked whether a change in the same child’s hours changed that same child’s behaviour. The result was zero.

Why it is still worth knowing: because you will hear this argument, and you should know that the older studies found a link and the better ones found no evidence that the hours cause it. It is a reason not to assume more hours is better. It is not proof of harm.

And one thing that is not on this list at all

Staying at home does not put a child behind.

The same large study checked children’s language and thinking at one, two and three. Children cared for only by their mothers did not do worse than children in childcare.

Why this matters most: it removes the fear behind a lot of these decisions. There is no evidence that a child who does not go to nursery is missing something he needs.

Where this leaves us

All of this is real, but the points are not equal.

The illness finding is certain. The physical cost of a nursery day is real, though we do not know whether it matters in the long term. The undivided attention at home is a genuine advantage. The behaviour argument is much weaker than the internet suggests.

But notice something. Every point above assumes one thing: that home means a warm, attentive adult who talks to him, takes him outside and answers him when he needs something.

If home means an adult busy with housework, a television on in the background, few books and no other children, then every advantage on this list disappears.

Which is the same problem as before, from the other direction. The question was never nursery or home.

It is which nursery, and which home.

So I need to know what a good nursery actually looks like.

That is Part 4.

Most parents reach this question the same way. It starts to become too much. There is too much work, and you begin to notice that you are not giving the little one the time he deserves. Then one of you gets tired, and the other one follows, and there is nobody there to take over.

Then you begin to wonder two things. Would nursery help us? And would it actually be good for him?

Whether it would help us is obvious. Of course it would. That is why we are asking in the first place.

So I went looking for the harder question. Would it be good for him?

Here are five things the research found that make a real case for nursery.

First: a good nursery gives a child more language.

This is the clearest finding in the field. Children in better-quality nurseries had better language and better thinking at ages one, two and three.

And the reason was simple. In those nurseries, the adults talked to the children more.

Why this is a point for nursery: more talking produces better language, and a good nursery is a place where an adult talking to your child is the job rather than something fitted in between other tasks.

Second: a room full of people produces more talking than a room with one adult.

At home, the language a child hears is whatever one adult says to him.

At nursery, several adults are speaking. Other children are making sounds. There are songs and books and routines with words attached. And he hears everything said to the other children as well.

Why this is a point for nursery: the amount of language reaching a child goes up simply because there are more people in the room. Home cannot produce that no matter how good the adult is.

Third: other children teach him things adults cannot.

At this age, children do not really play together. That comes later.

But being around them still teaches him. Another child takes his toy, so he learns what that feels like. Another child copies him. He has to wait his turn. He has to make himself understood without the words.

And he watches other children and copies them. He sees one child use a spoon, then he tries a spoon.

Why this is a point for nursery: children learn by watching children slightly ahead of them, and at home there is nobody to watch. This is the one thing a parent genuinely cannot provide alone.

Fourth: he can gain another adult who is truly his.

Children can form real, secure relationships with nursery staff. Not a replacement for a parent. An additional adult who knows him, comforts him and answers him.

This only works if that adult stays. One study compared nurseries where staff stayed a long time with nurseries where staff changed often. Where staff stayed, children got more attention and had fewer behaviour problems.

Why this is a point for nursery: at home a child has the adults he was born to. A good nursery adds one more, and having more trusted adults in the world is a real gain for a small child.

Fifth: fewer children per adult means more attention.

Nurseries with better numbers had children with better language and fewer behaviour problems.

An adult looking after three children can watch one of them, notice what he wants and respond to it. An adult looking after ten cannot.

Why this is a point for nursery: a well-staffed nursery room is designed around children. A home day is not. If the numbers are right, the attention is deliberate rather than whatever is left over after the cooking and the laundry.

Where this leaves us

All five are real and based on research in child development. And all five depend on one thing, which is the same thing I found in Part 1.

They only happen if the nursery is good.

None of them come from the building, the sign on the door, the uniform or the curriculum. They come from what the adults in that room actually do all day. A bad nursery gives none of this. An average one gives very little.

There is also research pointing the other way, and I am not going to skip it because it makes the decision harder.

That is Part 3.