In the U.S. it is not uncommon for students to get a grade of less than A-minus.
The reason is often because of the poor quality of the teacher's education. In Sweden, it is more common to get an A- or B- grade. The problem is that the teachers don't have enough time to teach all the students. In the UK, it's more common for the schools to teach the students to learn how to do it without the teacher. The teacher must also be able to supervise the students, which is difficult.