What is the correlation between Grade Point Average (GPA) and intelligence?
Assessing Adolescent And Adult Intelligence (Kaufman &amp; Lichtenberger, 2005) goes through quite a bit of the research on this.  Or you can use the correlation of 0.7 that they report, which is based on an aggregation of more recent studies of adult intelligent test scores and academic achievement.  I don't see where they break down country, but they do look at level of schooling a bit.  Perhaps some of their sources will help.