Do trees make children smarter? It’s complicated.

A number of recently published studies suggest that children exposed to more vegetation or greenery — in their home neighborhoods, daily commutes, or around their schools — exhibit improved cognition. For example, schoolchildren in Barcelona with more exposureto greenery exhibited improved cognitive development, better attention, and higher volumes of gray and white matter in important regions of the brain. Researchers have found a similar relationship between greenery and spatial working memory for children in the UK. In a related body of research, several studies have documented the positive effects of greenery around schools on academic performance, as well as of lessons in nature on classroom engagement.

It was suggested that the results could be driven by vegetation’s mitigating effect on environmental stressors (noise or heat, for example), or by a reduction in emotional arousal brought about by green spaces. These findings, which suggest a role for straightforward interventions to increase neighborhood greenery, have excited many in the field.

But a new paper by Aaron Reuben, a psychology PhD student at Duke University, and coauthors suggests the relationship between greenery and cognition may be complicated. The paper examines the relationship between neighborhood greenery and cognition among children in the UK, but differs from previous work in several important ways. The researchers studied the relationship over a longer time period than in previous studies, and they used a more general measure of cognitive ability. Finally, they included an additional control to account for the possibility that families with a genetic predisposition toward advanced cognitive development may self-select into neighbors with more greenery. They also used a particularly rigorous measure of social class, effectively controlling for socioeconomic factors.

Consistent with previous studies, Reuben and his colleagues found that children who grew up surrounded by more greenery did in fact outperform their peers on cognitive tests, at all ages. The effect, however, disappeared completely after the researchers controlled for the socioeconomic characteristics of children’s families and neighborhoods. “Children raised in greener neighborhoods exhibit better overall cognitive ability,” the researchers conclude in the paper, “but the association is likely accounted for by family and neighborhood socioeconomic factors.” The relationship between greenery and cognition seems to be complicated.

“It’s still an open question whether exposure to a natural setting fundamentally influences overall cognitive ability. Maybe it just provides a short benefit for attention.”

“Our results suggest we should view previous results with caution,” Reuben says. “But I don’t think our results invalidate theirs. Our results simply say that it’s more complicated than just: greenery is good for the brain.” Reuben says the conflicting findings suggest a need for more research on the topic, particularly with respect to long-term cognitive outcomes. He notes that while the research on the learning benefits of lessons in nature, or providing learners with a break in nature, is compelling, it remains unclear whether those benefits provide long-term cognitive boosts.

“It does seem that exposure to a natural setting can refresh you and allow you to pay attention in class or hold a few chunks of information for a few seconds longer,” Reuben says. “But it’s still an open question whether that fundamentally influences overall cognitive ability. Maybe it just provides a short benefit for attention.”

Reuben also says he’s particularly interested in the growing field of research on how greenery affects mental health, and perhaps ultimately cognitive outcomes. “There seems to be some instinctive psychological benefit to being in or around green spaces,” Reuben says, “and that is a finding that cuts across socioeconomic lines and may matter even more in the most disadvantaged communities.”

“There seems to be some instinctive psychological benefit to being in or around green spaces, and that is a finding that cuts across socioeconomic lines and may matter even more in the most disadvantaged communities.”