Actually, Picture Completion is vulnerable to vision issues as well (test of attention to visual detail, among other things). So is Coding, which he did well on. I wonder why the alternative PRI subtest of Picture Completion was administered, instead of the standard Picture Concepts subtest. The latter is a better measure of fluid reasoning (which might have been more in line with Matrix Reasoning).
It might have been informative if the psychologist had reported whether his BD score changed when scored without bonus points for time (de-emphasizes speed in scoring).
And yes, formal achievement testing would be considerably different from the classroom and group testing that he likely experiences at school. It is individually-administered, and should cover a range of higher-level and lower-level academic skills, such as in reading (decoding skills and comprehension), writing (spelling, written expression, and possibly handwriting), and mathematics (computations and problem solving).
