I seem to have attributed a different cause to this correlation than most other HN'ers in the comments. Is it possible that the isolation of the older child pla

I seem to have attributed a different cause to this correlation than most other HN'ers in the comments. Is it possible that the isolation of the older child plays more of a role in the higher test scores than the 2-3 years of undivided parental attention? The older child would grow up without an always available "playmate", and this seems like it could lead to more reading and eventually higher test scores. This same effect could also apply to lone children. Note: I'm not saying this isolation is a completely good thing (child may not have as good of an opportunity to develop strong social skills).