This study of four cohorts of French schoolchildren shows that the gender gap in math (girls falling behind) begins essentially immediately as soon as kids start school. They use the natural variation in kids' ages at school start to show that it's school entry, not age, that triggers the change.
Boys and girls exhibit very similar maths scores upon school entry, but a gender gap in favour of boys becomes highly significant after 4 months of schooling, which increases with years of schooling,&...
