Short-sightedness (also called “myopia”) is more common amongst children with higher school exam grades and those who go on to university. There are many potential reasons for this link, such as, (1) too much school work may cause short-sightedness, (2) short-sighted children may be more studious or “bookish” and therefore perform better at school than children with good eyesight, (3) one or more outside factors may cause both short-sightedness and better school performance. Conventional studies of the relationship between education and short-sightedness cannot answer whether options 1, 2 or 3 above is/are correct. Therefore, instead, we propose to use a method called “Mendelian randomisation” that is able to find the answers to this question. Mendelian randomisation uses naturally-occurring genetic differences between individuals to identify children who are – because of their genetics – very slightly more likely than average to become short-sighted, or very slightly more likely than average to do well at school. The technique works by examining the school performance of children who are slightly genetically predisposed to become short-sighted, and examining the eyesight of children who are slightly genetically predisposed to do well at school.