I think “applying for Oxford” is doing more work in that sentence then you give it credit for—it isn’t a random sample, it’s already skewed to only include those 17 year olds for whom the relative age effect wasn’t enough to stop them from performing well in school. One of my freshman year roommates at Harvard, and probably the smartest of us all academically, was 16, having skipped grades—obviously these people exist, and obviously people like parents, teachers, and guidance counselers are already steering students towards applying to schools that match their ability levels at the start of senior year of high school.
The comparison I care about (and that age cohort studies are trying to approximate) for this question is how much more those 17 year olds would have learned, over the course of all their years of schooling, if they’d been a little older at the very beginning. To look at that, I’d want to see, for example, whether the proportion of students applying to Oxford, or becoming valedictorian of their high school class, are more likely to be older or younger.
I think “applying for Oxford” is doing more work in that sentence then you give it credit for—it isn’t a random sample, it’s already skewed to only include those 17 year olds for whom the relative age effect wasn’t enough to stop them from performing well in school. One of my freshman year roommates at Harvard, and probably the smartest of us all academically, was 16, having skipped grades—obviously these people exist, and obviously people like parents, teachers, and guidance counselers are already steering students towards applying to schools that match their ability levels at the start of senior year of high school.
The comparison I care about (and that age cohort studies are trying to approximate) for this question is how much more those 17 year olds would have learned, over the course of all their years of schooling, if they’d been a little older at the very beginning. To look at that, I’d want to see, for example, whether the proportion of students applying to Oxford, or becoming valedictorian of their high school class, are more likely to be older or younger.