A third child will spend a year less in education on average than a first child, according to Professor Kjell Salvanes of the Norwegian School of Economics and Business Administration, who conducted an analysis of the link between birth order and achievement.
The study looked at the entire population of Norway who were aged at least 25 in the year 2000.
Professor Salvanes said: "There is a lot of psychological literature on why first-born children are most successful. The main suggestion is that the eldest child acts as a teacher for the younger children and learns how to organise information and present it to others. But, if resources are limited, it could be that the parents invest more in the eldest child."