Staying in school really can make you smarter. A new study from Norway finds that students who remain in school longer than their counterparts have higher IQ scores.

In the mid-1950s, the Norwegian government began requiring students to attend school until they were 16 years old, rather than allowing them to drop out at 14.

Communities had until 1972 to phase in the compulsory education reform, which meant that, for nearly 20 years, youngsters in some municipalities went to school for seven years and others attended classes for at least nine years.

That gave Taryn Ann Galloway a unique opportunity to see what impact the extra two years of education had on the intellectual development of students. Galloway, a researcher at the University of Oslo, explains that all young men in Norway are required to undergo a cognitive assessment, or IQ, test for the military draft at age 19.

So, she and her colleagues were able to sift through data on 107,000 draft-age young men, correlating their years of education with their IQ scores obtained by the military.

“The young men who were forced to stay in school for two years longer actually did have higher IQs," Galloway says. "So, based on that, we were able to say that increasing compulsory schooling did actually have an effect on their cognitive abilities as measured at 19 years of age.”

The average IQ score on the intelligence test is 100, with most of the population falling somewhere between 85 and 115 on the scale.

According to Galloway, students who got a full two years of extra schooling showed an IQ gain of more than 7 points. Those with just one additional year of compulsory education during the phase in period gained approximately 3.7 IQ points.

“So, that’s still quite large," she says. "They’re going from about average to well above average if they were affected by reform.”

For years, there’s been vigorous debate among psychologists about whether a person’s intelligence is the result of “smart” genes or a nurturing environment in infancy. Galloway’s results seem to support the nurturing side of the nature versus nurture argument.

She suggests getting two extra years of academic practice during the middle teenage years may also help boost IQ scores.

“I think it’s because you do learn general thinking skills at school and you are able to practice them, and you have lots of opportunity to practice them. So this is a two year extension of compulsory schooling for two years, so they were able to simply improve their skills.”