To measure educational aspiration, Bu looked at children’s responses to this question at age 13: “Do you want to leave school when you are 16, or do you plan to go on to sixth form or college?” Future waves of the longitudinal surveys followed up with these children to see the highest level of education they achieved. (Some of the research subjects aren’t yet old enough to have completed college degrees, so she measures instead whether they “gained any qualifications following the end of compulsory schooling.”)

As you might predict, firstborns had greater educational aspirations than their younger siblings—typically they were about 7 percent more likely to want to stay in school. Firstborns were also about 16 percent more likely to gain higher educational qualifications. (However, the spacing of the siblings did seem to have a buffering effect here—“the wider the age gap is, the more likely that individual attains further education,” the study reads.) The firstborn advantage was significant both within families and across families.