In the study, published in a September issue of Proceedings of the National Academy of Sciences, researchers looked at the performance of over 6,000 sets of twins on the General Certificate of Secondary Education (GCSE), a standardized test taken by 16-year-old students in the United Kingdom. The question the researchers wanted to answer was: How much of a role do genetic traits play on students’ achievement? They administered a survey to the twins, 35 percent of whom were identical twins with the same DNA. The rest of the twins were fraternal with 50 percent genetic similarity, some same-sex twins and others twins of the opposite sex. The researchers assumed these twins had been raised together with similar upbringings and schooling.

Previous studies have shown that innate intelligence plays a big role, but the researchers wanted to address the influence of other genetically influenced traits, such as personality, health, and behavior problems. They found that intelligence played the largest role, but the other eight categories of factors were important, too—in fact, much more important than previously anticipated. “The main finding is that, although intelligence accounts for more of the heritability of GCSE [test scores] than any other single domain, the other domains collectively account for about as much GCSE heritability as intelligence,” the study authors write.

But Judy Johnson, an educational psychologist based near Los Angeles, thinks that the authors’ conclusions are overstated. Most people in the field of educational psychology subscribe to the theory of multiple intelligences, which can be inherited, Johnson admits. However, she adds, “In terms of achievement, attachment theory has much more to do with a student’s engagement with teachers, school, and cognition.”