I’ve written about school size before, in talks and in books. About how some studies suggest there might be something like an optimal range. Not too large, because anonymity becomes a risk. Not too small, because it becomes harder to professionalise as a team, share expertise, and sustain a strong curriculum.

And then there is one exception I usually mention. The small secondary schools in New York.

That case is interesting because these schools are not simply “smaller.” They are the result of a deliberate reform that broke up large, struggling schools into smaller, themed schools with a clear focus on relationships, relevance, and academic expectations. And perhaps even more interesting, these schools have been studied quite extensively over time.

There is now new longitudinal research that adds another layer to that story. And not just any study. It uses lottery-based admission. Students who are admitted to these small schools are compared with those who just missed out. Methodologically, that brings you close to an experiment, which is rare in education, especially for questions like these.

So what do we see?

Students who attend these small schools are clearly more likely to graduate and to enrol in higher education. The effect on entry into higher education is about 9.5 percentage points. There is also a positive effect on obtaining a bachelor’s degree, although it is much smaller, around 2 to 3 percentage points. These are not spectacular numbers, but in education research, they are meaningful. Especially because they appear consistently over time and without additional cost per graduate.

But the story does not end there.

The researchers also looked at labour market outcomes. Those hoping for a clear effect will be disappointed, at least for now. There are no significant differences in employment or earnings in the first years after secondary education. That may mean there is no effect. But it may also be too early to tell. Many of these students are still in higher education, and we know that wage differences often only emerge later.

There is another important finding. The effects are not equal for all students. Those who were already stronger at the start, for example, in mathematics, seem to benefit more than those who started out weaker. That is not a minor detail. It reminds us that even well-functioning interventions can increase inequality. It brings to mind the work of Dietrichson and colleagues, showing that many educational interventions tend to widen gaps rather than close them.

So what does this mean for the debate on school size?

The temptation is to say: there you have it, smaller works. But that would be too simple. What this study really shows is that “small” in itself is not a magic solution. What seems to work are the conditions that smaller schools make possible: stronger relationships between teachers and students, more coherence in expectations, and a clear focus on academic quality.

Those conditions are easier to organise in smaller settings. But that does not mean they are impossible in larger schools. It does mean they need to be more deliberately organised.

And that brings us back to that “optimal range.” Perhaps we should take it less literally as a question of numbers and more as a design question. When is a school small enough for students to be seen, and large enough to sustain quality?

The small schools in New York show that it can be done. But they also show something else. Success rarely lies in a single visible feature. That is true for almost everything in education. Copying the form is easy. Understanding the design is the real work.

Image: https://commons.wikimedia.org/wiki/File:Seward_Park_High_School.jpg