Grade level in Vietnam
Grade level and age: http://en.wikipedia.org/wiki/Education_in_Vietnam#School_grades
picture reference: http://www.business-in-asia.com/vietnam/education_system_in_vietnam.html
More to the point: Secondary education (Vietnamese: trung học phổ thông) consists of grades ten through twelve. The IGE is a prerequisite entrance examination for secondary schooling. The IGE score determines the schools at which students are able to enroll. The higher the score, the more prestigious the school.
So, unlike the U.S. where everyone is passed along until they're 18 years old, in Vietnam they thin the herd as you progress. So, if Google steps into a classroom, it's likely seeing the top of the top, and even all those won't get into public University. Private is expensive for most to attend.
Also, Calculus is taught in grades 11 and 12.