B. 15%, percent of all students in grade 6 at HACS are below grade level in math.
The information states that the math test was administered to all students in grade 6 at High Achievers Charter School and it was found that 15% of them were below grade level in math. Therefore, we can infer that 15% of all students in grade 6 at HACS are below grade level in math. However, we cannot make any conclusions about the students in other grades or the entire student population at HACS.