What is the plural form of the letter A, as in the grade or mark, not the indefinite article?

Question

This is a line from the tutoring job on my resume.

Helped raise 12 students’ grades from Cs and low Bs to high Bs and A’s in multiple classes across different semesters.

Is the plural form for A correct? I think an apostrophe is needed to prevent confusion with the word "as."

Answer 1

You do not need the apostrophe because (i) from Cs and low Bs to high Bs and as in multiple classes across different semesters does not make sense and (ii) as has no capital letters. The apostrophe in A's also looks strange as you have not used it in Cs and Bs