Underperformance caused by large classes
Sociologist compared IQ scores of primary school children with maths test scores
Children in primary education perform less well than they could based on their IQ score. This is what sociologist Deni Mazrekaj at Utrecht University found. “We measured underperformance. This shows that children in primary education do not use around a quarter of their potential.” Mazrekaj’s findings were recently published in the academic journal Exceptional Children.

The Utrecht sociologist and his colleagues Kristof de Witte and Thomas Triebs observed 2,228 children in 168 different Flemish schools for over the course of 6 years. Mazrekaj: “We used a method known as Stochastic Frontier Analysis. This method estimates, based on the IQ score achieved, what a child ought to be able to score in a maths test. We then compared this result with the maths test score that the pupil actually achieved.” The average ‘underperformance gap’ turned out to be 23.5%: on average, this means that almost a quarter of the child's maths potential is not utilised.
We found that underperformance is minimal with a class size of about 20 pupils
Class size plays a decisive role
Underperformance is not something that happens to a specific group of children. “It concerns all children, including the highly gifted,” clarifies Mazrekaj. According to the sociologist, class size is a determining factor when it comes to underperformance. “We found that underperformance is minimal with a class size of about 20 pupils.”
Policymakers and lecturers
His research results provide food for thought for both policymakers and teachers. Mazrekaj points out that policymakers need to take account of the fact that children do not utilise much of their potential. “And it is probably also good for teachers to realise that even pupils who always score well in tests can likely do better still.”