Question

The gender gap in math performance varies within and across countries. the countries with the smallest difference between their male and female students are those with

Answer 1

The term gender gap denotes the disproportionate difference or disparity between the sexes, between males in females.The bigger the gap, the bigger the difference between genders and the smaller equality between the.The smaller the gender gap on the other hand the greater the equality between genders. 
The countries with the smallest difference between their male and female students are those with the greatest degree of overall gender equality.