Perhaps I am not precisely understanding your explanation, Archie.
Regardless, the grade equivalents on the WIAT do mean that the student obtained the same raw score on the measure that the median (in this case) 11th grade, 9th month (nearly grade 12, IOW) student did on the same subtest in the standardization sample. As the test includes tasks of skill level roughly prekindergarten through high school (though he probably was able to skip over the easiest items), it is highly likely that a score at this student's reported performance level would have included correct answers on tasks above the third grade level. I can say this with a high degree of confidence, as I have administered and interpreted this instrument myself hundreds of times. In any case, the bottom line remains that using a grade equivalent is not recommended for meaningful interpretation of this kind of test.
From your description, I assume the website you reference is Ron Dumont's FDU page.
His website (with John Willis, also a major figure in the field)
www.myschoolpsychology.com is an excellent source of information on assessment and many other topics in psychology. There he links to Pearson's official statement on age/grade equivalents, adhered to by all reputable assessment professionals:
https://www.pearsonclinical.com/lan...oblems-of-age-and-grade-equivalents.html
