Its not always true. Even boys perform outstandingly in academics equivalent or more to girls.
Consider the difficult engineering/medical entrance exams - where boys always outshine girls. Example : In IIT-JEE '09 itself out of 4 lakh candidates who appeared, only 1048 girls qualified and remaining 8987 who qualified were boys.
Same goes with medical.
Its true that girls have been performing better than boys in board exams. But than this does not mean that boys are less good in academics or girls are more.