In Israeli schools, grades are not known by number but by letter; e.g., 'grade a' = 1st grade, 'grade b' = 2nd grade, etc. Most schools have more than one class in each grade, and the classes are known by number: class d1 means the 1st fourth-grade class in the school. (The numbering is arbitrary: class d2 isn't necessarily worse or better than class d1.) Typically, children retain their number throughout their school career: e.g., the children in class c4 become class d4 the next year.
I had the following conversation (in Hebrew) with a strong chess player I know.
Me: By the way, what grade is your daughter in school?
Him: She's in the English opening.
Me: Next year the Queen's gambit, I suppose?
Him: Yes. The year after that, the Ruy Lopez.
Me: And then Bird's opening?
Him: Well, that's a rather doubtful opening, isn't it?
Me: That's what they're all like when they're 12, I've heard.
And they say chess players live in a world of their own.