I assume that the 11th grade math score you mentioned is a grade equivalent (GE). This means that his achievement is the same as that of an 11th grader at the 50th percentile. This sort of score is actually fairly typical for gifted kids at your son's age, especially if they have unlimited time. A GE of 11.9 is essentially mastery of 4th or 5th grade math.
Actually, grade equivalent means that her son scored the same as an 11th grader did in his grade level maths. It does not mean that her son is at an 11th grade level in maths.
