How many students in your school do you know by name? 

Chances are, the number will be between 100 and 150. You would probably reach a similar or even lower number if I asked you to list the “meaningful” relationships in your life - for example, to create a wedding invite list.
 
This number has an anthropological basis, according to evolutionary psychologist Robin Dunbar. In the 1990s, his research led him to 150 as the number of stable relationships most human beings can comfortably maintain. Dunbar explained this as being the “number of people you would not feel embarrassed about joining […] for a drink if you happened to bump into them in a bar”.
 
While we hopefully won’t bump into too many students in bars, if we were to translate Dunbar’s figure to the school environment, we might think of it as the number of students who, when we meet them in a corridor, we can confidently greet by name and ask after a sibling, or comment on their recent performance in a school concert, sports match or assembly.

I first heard about Dunbar’s research on a podcast, heading home from the small school I teach at. As I listened, I found myself thinking back to the year I began my teaching practice in a school so large that, when I left, the headteacher handed my leaving card to a different English teacher.
 
After this, I moved steadily away from mainstream and into special educational needs and disabilities (SEND) teaching. As I did so, the schools I taught in decreased in size, until I reached the school I teach in now, which has just 150 students on roll and seven to nine students in each class. There aren’t any students in the school I don’t recognise, and only a handful I don’t know by name.

The majority of mainstream schools, however, often greatly exceed 150 students, and I began to wonder if this is something we should be concerned about. 

According to 2020 research commissioned by the NEU teaching union and led by researchers at the UCL Institute of Education, one in four young people feel they do not “belong” in school - a figure that is rising. This is a problem, the report finds, because a sense of belonging has been linked to increased motivation, higher attainment and reductions in absenteeism, as well as other positive social outcomes. Young people who “experience a sense of exclusion from school”, meanwhile, are more likely to “seek ‘belongingness’ elsewhere” - perhaps in places we might not want them to look for it.

This got me thinking: could Dunbar’s number and the sense of alienation that some students feel be connected? And if it is, are there ways for us to reframe school communities to nurture that sense of belonging? Or, do we just need to rethink the size of our schools?

These are complicated questions, so I set out to look at the research evidence, starting with Dunbar. 

Writing recently in The New Scientist, Dunbar explains that he reached his number through extensive research into the social habits of primates. 

“In monkeys and apes, there is correlation between primate brain size and the size of their social groups, and by extrapolating this relationship, we would expect humans to have a natural upper limit to the number of people in their group to about 150,” he explains. 

“Although an individual’s social network may include many more people, 150 contacts marks the cognitive limit on those with whom we can maintain a stable social relationship involving trust and obligation - move beyond 150 and people are mere acquaintances.”

There is an evolutionary basis for this number, but, Dunbar continues, there is also a historical precedent.

“Historically, [150 people] was the average size of English villages. It is also the ideal size for church parishes, and is the size of the basic military unit, the company,” he says. 

In his recent research, Dunbar has looked in more detail at how his findings relate to church congregations. In a 2020 study with Roger Bretherton, he found that the sense of belonging felt by the members of a congregation was connected to the number of people in that congregation. 

The sense of investment in the community peters off as congregations expand to exceed 150 members, and those congregations become “self-limiting”. In other words: if the congregation gets too big, people just stop attending. 

Of course, this doesn’t tell us anything definitive about how school size might affect pupils’ feelings of belonging. 

But one thing we do know is that many schools are getting bigger. According to government data, the average number of pupils in a state-funded secondary school is now 1,027, up from 939 in 2015-16. We have also seen an increase in “supersized” secondaries - those with more than 2,000 pupils on roll. 

And while the number of schools operating over capacity has actually decreased slightly in the past couple of years, there are still significant problems here, with 22 per cent of secondary schools and 17 per cent of primary schools in England over capacity.

But is the size of our schools actually something to be concerned about? 

The government, it seems, do not see large schools as problematic. Back in 2015, the then schools minister Nick Gibb supported councils’ plans to establish more supersize schools, citing the success of schools in East Asia.

“If you look at Shanghai, their schools are very large and they produce some very high standards of education,” he told Tes at the time. 

More recently, Ofsted has been accused of rating small schools more harshly than larger ones; as a Tes analysis revealed last month, England’s smallest primary schools are five times more likely to be rated “inadequate”. 

Unfortunately, high-quality studies looking at the connection between school size and student outcomes are slim on the ground. 

One 2015 US study, conducted by Seth Gershenson and Laura Langbein, found that evidence on optimal school size is mixed. The pair reviewed existing evidence and then analysed data from administration records for 3rd to 5th grade (Years 4 to 6) pupils in state schools in North Carolina between 2003 and 2010.

They found that, on average, there was no causal relationship between school size and academic performance. However, there were two groups of students who appeared to be “significantly harmed by [larger] school size: socioeconomically disadvantaged students and students with learning disabilities”. 

“The largest effects are observed among students with learning disabilities,” the researchers explain. “A 10-student increase in grade size is found to decrease their maths and reading achievement by about 0.015 test-score standard deviations.”

In the UK, meanwhile, Mark Newman and colleagues conducted a systematic review in 2006 of 31 studies looking at the effects of secondary school size from Organisation for Economic Cooperation and Development (OECD) countries since 1990.

They found that, overall, the patterns of effect vary depending on which outcome you are looking at.

“For pupil attainment measured by exam results, and for attendance, larger schools appear to do better up to some optimal school size, but estimates of this point or range are insufficiently precise to be useful,” the researchers state. “The implications of different school sizes on student behaviours are equivocal, but teachers and pupils at smaller schools are more likely to have a positive perception of their ‘school environment’. Costs per pupil appear to decrease as school size increases.” 

Overall, the team concluded there was not enough evidence to suggest we should be aiming to mandate particular school sizes. However, they add, “given the evidence that there do appear to be optimal sizes for some outcomes, stakeholders should be made aware that dramatic changes in a school’s size may change the characteristics of a school’s learning environment”.

The evidence linking school size to positive outcomes is limited, then. But it seems to me that there is still enough to warrant further study, particularly when it comes to the issue of belonging.

While a larger school might be more cost-effective, in my experience, as the school gets bigger, students and staff feel less connected and less valued. The risk is that in a bigger school, no one, except perhaps those at the very top, feels invested in the whole. Wellbeing declines and behaviour problems escalate.

Indeed, in my teacher training year at a “supersized” academy, I have a vivid memory of hearing a loud rattle outside my classroom. I peered through the door to see unfamiliar students using a wet floor sign as a skateboard and pelting down the staircase on it. 

As a nervous trainee, I did the exact opposite of what you might hope a teacher would do in this situation: I stepped back and closed the door, hoping these unknown students wouldn’t see me.

There are those, of course, who would blame such issues on the schools’ systems and culture, rather than their size - and they may be right.

There are some interesting talking points in the data on absences and exclusions in the DfE data on this issue. The DfE classes a large school as more than 300 pupils in primary and 1,200 pupils in secondary, and a small school as less than 200 pupils in primary and less than 700 pupils in secondary.

Large schools and small primary schools have roughly the same levels of unauthorised absence, but large primary schools have a higher proportion of students with persistent absence problems (8.2 per cent versus 9.2 per cent in 2021; 8.4 versus 8.9 per cent pre pandemic in 2018). In secondary schools, however, smaller schools have significantly more persistent absence than large schools (16.5 versus 13.6 per cent in 2021) and very marginally more unauthorised absence.

For exclusions and suspensions, there is no difference in primary schools of different sizes on the rate of exclusions, but large primary schools have a slightly higher rate of suspensions. In secondary, smaller schools have had higher rates of both exclusion and suspension over the past five years.

What can we take from this? Data for both these areas is notoriously noisy, but it does appear smaller secondary schools have more problems with behaviour and absence than larger secondary schools.

So, if size matters, perhaps it is class size, rather than the size of the school we should be paying attention to.

Class size is certainly an area where we have more extensive evidence about the impact on pupils’ attitudes and attainment.

The Education Endowment Foundation’s Teaching and Learning Toolkit finds that the average impact of reducing class sizes is around two months of additional progress, if the class is reduced by ten pupils or more. 

However, small reductions in class size, for example, from 30 to 25 pupils, are “unlikely to be cost-effective relative to other strategies”, the toolkit states.

There is also some evidence that smaller classes might be more effective with younger children and with disadvantaged learners. But the key is for the class to shrink enough for the teacher to “teach differently - for example, having higher quality interactions with pupils or minimising disruption”, the toolkit explains.

“When a change in teaching approach does accompany a class size reduction (which appears hard to achieve until classes are smaller than about 20) then benefits on attainment can be identified, in addition to improvements on behaviour and attitudes,” it continues.

When it comes to class size, then, there is some evidence that smaller is better. 

However, the EEF also warns that this evidence is “very limited, so should be treated with caution” and points out that the costs associated with reducing class sizes enough to make a difference will be prohibitive for most schools. 

So, if creating smaller classes isn’t a realistic option, what else could schools try to maximise the sense of belonging their pupils feel?

One option might be to look at how they can use Dunbar’s number to rethink their communities.

In Dunbar’s study into church congregations, he found that in order to “retain active member involvement” within a large congregation, members needed to be split into smaller “sub-divisions”. 

Perhaps we could apply this principle to the formation of pastoral groups within schools, with 150 being the maximum number of pupils in a house, for example. 

If intake allows, you could also consider limiting year groups or key stages to 150 pupils - or, failing that, creating two halves to the year group or key stage, making it more explicit that these are communities and providing more opportunities for the pupils within them to share time and experiences.

For extracurricular activities, it could likewise be worth considering reducing the size of groups, allowing students to build stable relationships more easily with peers and with staff. Rather than one whole-school drama club, for instance, is there a way to create two?

Some schools take this idea of small communities even further. Tor Bridge High in Plymouth, for example, operates a system of “schools within a school”: four small schools, each made up of about three hundred students, with their own head of school and staff team. The schools are described as “home bases” built around a “family” atmosphere that allows staff and students to build strong relationships.

And there are other steps to consider, too. 

According to a 2017 analysis by the OECD, which looked at students’ sense of belonging in schools based on the 2015 Programme for International Student Assessment results, teachers and school leaders can try to “put in place strategies to identify those students who are most at risk of social exclusion and provide them with the means to establish positive social ties with educators and peers”.

Regularly collecting feedback from students on how they view the learning climate and the relationships they maintain at school might be one way to do this.

The report stresses that supportive relationships with teachers and a disciplined and fair learning environment are also key. It adds that teacher training or CPD focussed on “emphasising communication skills, the ability to manage behavioural problems and pedagogical approaches to establish positive and supportive relationships” could help here.

I would add that while it is not realistic to restrict all schools to 150 students, finding ways to create groups within the school that do not exceed this size could go a long way towards forming those relationships.

After all, when a student walks between lessons and is greeted by a teacher by name, they’ll feel more like a part of the whole.

And when a teacher sees students mucking about in the corridor - or sliding down the staircase on a homemade skateboard - knowing those pupils by name will make addressing their behaviour a whole lot easier, whether you are an anxious trainee or an experienced member of staff.

Clare Deal is a SEND teacher working in Newcastle