This is because you are measuring the entire cohort/generation of students. Germany splits students into highschool (called Gymnasium, the academic track) and

This is because you are measuring the entire cohort/generation of students. Germany splits students into highschool (called Gymnasium, the academic track) and the vocational tracks at age 10. Smart-kid highschool in Germany definitely moves faster than US highschools. Some even teach Greek and Latin for a well-rounded humanist education.