A mother works with her son on his homework in this file photo.(Image via AP Photo/Toby Talbot)

Think a mother’s age at childbirth plays any role in her child’s intelligence? According to data on British kids, it sure does. Using information on 18,000 children gathered over “an extended period of time,” researchers from the London School of Economics say kids born to first-time moms in their 30s have better cognitive scores and “behavioral outcomes” than first-born children with mothers in their 20s, theIndependent reports.

“First-time mothers in their 30s are, for example, likely to be more educated, have higher incomes, are more likely to be in stable relationships, have healthier lifestyles, seek prenatal care earlier, and have planned their pregnancies,” lead author Alice Goisis tells the Timesof London. These kids also outperformed children whose moms were in their 40s.

Published in Biodemography and Social Biology, the study also found that children born to women in their 40s are more often obese because their moms don’t play with them as much. This despite the fact that moms that age typically smoke less and breastfeed their kids, Marie Clairenotes. But researchers acknowledge they culled data from only 53 mothers in their 40s.

There’s also the question of what defines intelligence: “Of course kids who have parents with more resources to offer (i.e., good schools, tutors, even high-quality nutrition) are going to do better when it comes to school and tests. But are book learning and intelligence really the same thing?” asks Jacqueline Cote at Cafe Mom. “And I’m not saying that simply because the two children I had in my 20s are honor students! Really, I’m not.” (In the US, more women are waiting until their late 30s to have kids.)