Want to get your kids to the top of the class? One economist says the secret may lie  in the age gaps between siblings. Having at least two years between brothers and sisters makes for better math and reading scores.

Kasey Buckles, an economist at University of Notre Dame, and  Notre Dame graduate student Elizabeth Munnich surveyed more than 12,000  people between the ages of 14 and 22 from the National Longitudinal Survey of Youth. The research, published in the Journal of Human Resources,  found that  when age gaps between siblings were greater, the older child performed better on math and reading achievement tests. Low-income families benefited most from age spacing. First-born siblings also showed the most benefit when there were greater age gaps.

“On average, a one-year increase in spacing improves reading test scores by 0.17 standard deviations, and there seems to be an even greater benefit to avoiding spacing of less than two years,” said Buckles, who has two children, two years and two months apart. “We find no evidence that the spacing affects the test scores of the younger sibling.”

Study authors said parents read to the older sibling and kids watched  less TV when the age spacing was greater.

Parents who consider having more children often wonder whether it’s better to have them closer together in age or further apart, said Buckles. Some believe kids should be close in age so they can play together, but others suggest more space so that the older child can become more independent.

The study confirms that the more productive  time parents spend with their children, the more advanced the kids’ academic achievement will be, said Rahil Briggs, assistant professor of pediatrics at Montefiore Medical Center in New York. It is easier to spend productive time with one child, one-on-one, than with multiple children, which could explain the findings.

Children’s language normally flourishes in the second year of life. They go from one or two words at age 1 to at least 50 words by age two, and then hundreds of words by age 3 with properly constructed sentences, said Briggs.

“The single biggest predictor of child vocabulary size at age 3 is number of words spoken to the child before that time,” said Briggs. “If parents are spending most of their time with an infant, it’s likely that their spoken language to the first child, right in the middle of their language explosion, is decreased.”

But before all of you siblings close in age (like my two sisters and me) get discouraged about the spacing, Briggs said randomized clinical trials with families perfectly matched in everything from health to finances are needed to substantiate the results.

“It is the age old  ’correlation does not equal causation,’” said Briggs.

No matter the age spacing, Briggs said if parents want to make sure their kids are on path  to academic achievement, “read to your child, read to your child, read to your child. Talk to you child, talk to your child, talk to your child from day one. Expose your child to the learning opportunities present in every day interactions.”