One of the key conclusions is that temperament – often seen as innate and stable – can change more than has longbeen assumed. Huijzer-Engbrenghof focused on negative emotionality as a component of temperament: children's tendency to react strongly to frustration or stress. ‘This can be an important predictor of how children cope with situations later in life,’ she says. High negative emotionality, for example, is linked to problems in relationships and at work in adulthood.

Huijzer-Engbrenghof investigated whether parenting interventions designed to reduce disruptive behaviour can influence negative emotionality. ‘What we found is that not only did children's disruptive behaviour decrease, but negative emotionality also decreased simultaneously,’ she says. ‘This could cautiously suggest that temperament isn't such a fixed factor after all.’

The role of parenting interventions

The study used, among other things, the "Incredible Years" parenting intervention. Parents participate in group training sessions where they learn to deal differently with their child's challenging behaviour. This is important, she says, because parents and children often find themselves in an escalating interaction. ‘They ping-pong back and forth, reinforcing each other's behaviour,’ she says. ‘If a child screams and whines and the parent finally gives in, the child learns that this behaviour works. Or if the parent screams, the child listens out of fear, and the parent then believes that harsh and strict parenting works.’ In the training, parents learn to give more positive attention, use compliments and rewards for good behaviour, and ignore disruptive behaviour more often, Huijzer-Engbrenghof explains. ‘This can break the vicious cycle.’

A fiery temperament does not necessarily provoke harsh parenting

Another question in the study was whether children with a fiery temperament elicit harsher parenting behaviour from their parents, such as yelling or belittling. This turned out not to be the case. ‘Negative emotionality and harsh parenting were predictive of more disruptive behaviour, but children's negative emotions did not elicit harsh parenting from their parents,’ says Huijzer-Engbrenghof.

Genetics are not a deal breaker

Genetic factors also proved to be less decisive than is sometimes thought. One study examined children's genetic predisposition to disruptive behaviour, calculated using so-called polygenetic scores. The expectation was that this predisposition could influence how well a parenting intervention works.

‘Even in children with a genetic predisposition to disruptive behaviour, we saw that the intervention was effective in reducing this behaviour,’ says Huijzer-Engbrenghof. ‘The children's genetic makeup had no influence on this.’

This doesn't mean that genes don't play a role, she emphasises, but it does mean that they don't make change impossible.

Early intervention offers opportunities

According to Huijzer-Engbrenghof, the most important message from her research is that parenting matters and that parents can indeed influence their child's temperamental traits, especially at a young age. ‘With very young children, you can still make a lot of adjustments before you end up in a vicious cycle and continue to reinforce each other's behaviour.’

At the same time, she emphasises that there are no simple solutions. Not all families benefit equally from interventions, and development remains an interplay between child, parent and environment. But the idea that a child "just is that way" is incorrect, she says. ‘There are plenty of strategies parents can use to positively influence a child's behaviour.’