How well is your child doing academically? Parents with concerns tend to focus on what’s happening inside the school (Are the teachers good? The class sizes small?), while also monitoring behavior at home (Is homework getting done?).

While both are important, a new study suggests there may be another, less-obvious factor at play: The walk or ride between home and school, and whether it involves immersion in the natural world.

Exposure to nature has long been linked to lower stress levels and mental alertness, but a new, first-of-its-kind study finds it is also associated with higher scores on a standardized test.

Even after controlling for factors such as race and parental income, Massachusetts third-graders with greater "exposure to greenness show better academic performance in both English and math,” reports a research team led by Chih-Da Wu of National Chiayi University in Taiwan. Its study is published in the online journal PLoS One.

There’s something intangible about exposure to the natural world that leads to a more relaxed state of mind. And a calm mind is, as a rule, likely to function more efficiently and effectively than an anxious one.

The researchers compared test results from 2006 through 2012 in 905 public elementary schools in the state. They specifically looked at the percentage of third graders in each school who scored "above proficient" in math and science on a standardized test conducted as part of the Massachusetts Comprehensive Assessment System.

They also used satellite imagery to measure the "greenness" surrounding each school. The researchers specifically calculated the amount of vegetation that was present in a 250-meter, 500-meter, 1,000-meter, and 2,000-meter circle around each of 905 public elementary schools. (Two thousand meters is about 1.25 miles.) The calculations were done in March, July, and October of each year.

Finally, they took into account a variety of factors that have been shown to influence test scores, including race, gender, parental income, a school's student-teacher ratio, and the percentage of students whose first language was not English.

"After adjustments for the available socioeconomic factors, surrounding greenness in March showed a very significant association with school academic achievement in English and math, regardless of which buffer difference was considered," the researchers report. "The results showed a consistently positive association between the greenness of the school in the spring (when most Massachusetts students take the MCAS tests) and school-wide performance on both English and math tests."

The specific reasons why exposure to nature could boost student performance remain somewhat elusive. The researchers cite, among other things, “increased physical activity, increased social contracts, reduced psychophysical stress and depression, decreased noise,” and lower levels of air pollution.

But many studies suggest there’s also something intangible about exposure to the natural world that leads to a more relaxed state of mind. And a calm mind is, as a rule, likely to function more efficiently and effectively than an anxious one.

This research suggests that maxim even applies to third-graders.