The way that teachers interact with their pupils affects learning over the long term. My study – co-authored with Alejandra Campos, Yyannu Cruz-Aguayo, Carolina Echeverri and Norbert Schady – is based on a massive, seven-year experiment in 204 schools in coastal Ecuador, where children were randomly assigned to different teachers in every grade from kindergarten (age 5) up to 6th grade (ages 10-11). This set-up is unique because it ensures that a child’s progress is actually due to the teacher’s quality, not because better pupils were paired with better teachers (Campos et al, 2025).
To measure lesson quality, we filmed teachers in action and used a coding protocol known as the Classroom Assessment Scoring System (CLASS). This tool looks at three main areas: how much instructional support a teacher gives; how they manage the classroom; and the emotional support that they provide.
We find that children who had teachers with higher-quality interactions performed better in mathematics and language tests. But the results also go beyond basic academic outcomes: these teachers also helped to improve a child’s ‘executive function’ – a set of mental skills that includes the ability to focus attention, remember instructions and juggle multiple tasks.
These benefits are persistent. While the boost from a good teacher might seem small in a single year, the gains stay with the child as they move through the school system. At the same time, we find no clear evidence that these specific teacher behaviours affected non-cognitive traits such as a child’s self-esteem, grit or levels of depression.
What constitutes a good teacher
For a long time, economists and education specialists have struggled to identify what actually makes a teacher effective. Characteristics such as having a master’s degree or years of experience often don’t predict how much children will actually learn. Our research shows that how a teacher interacts with children is a much more reliable measure of quality.
One of the most striking findings is that teacher quality is perfectly substitutable across grades. In the world of education research, there is often a belief in ‘dynamic complementarity’ – the idea that a good teacher in 1st grade makes a good teacher in 2nd grade even more effective. But our study suggests that this is not the case: instead, a great teacher helps a child just as much regardless of whether that child had a struggling teacher or a star teacher the year before.
Policies for teacher evaluation and support
Our findings have implications for how policy-makers evaluate and support teachers. Because classroom observations can predict pupil learning, they are a valuable tool for schools – especially in early grades like kindergarten where traditional test-based evaluations are difficult to perform.
Even so, while these interactions matter, the overall effect of a single teacher is relatively modest. This means that schools shouldn’t rely only on observation tools to decide who is a ‘good’ or ‘bad’ teacher, as this could lead to misclassifying staff.
Our study uses simulations to see if schools should move their best teachers to specific grades or assign them to the best or worst performing pupils. We find that it doesn’t really matter where the best teachers are placed: the total amount of learning in the school remains about the same. The most important thing is simply increasing the overall quality of interactions across all classrooms.
