The WCST is one of the classic executive function tests. The examinee sorts images on cards according to rules that one must figure out along the way. Periodically, and unexpectedly, the rules change, and the examinee must figure out the new rules. Many examiners use it to assess concept formation, cognitive shift (an EF skill), and maintenance of mental set (also an EF), among other things.
Although it is a venerable test, with a long and storied history in neuropsychology, its psychometric qualities are actually not as strong as one might think. The research finds that it does have good sensitivity to neuropsychological concerns, including ADD, ASD, and LDs, but not particularly good specificity, mainly because good/NT performance on it appears to involve many more parts of the brain than previously believed. The range of performance in normals is also pretty wide. In addition, the norms for children are not of the best, as they are relatively old (early 1990s), and relatively small (899 samples).
The value and meaning of the interpretation lie largely in the interpreter, and the other data obtained. For example, his difficulty with "trials to complete first category" could be a reflection of weaknesses in concept formation, or working memory, or sustained attention, or hypothesis testing, among other things. Where he also has a Dx of ADHD primarily inattentive, with provisional/rule-outs for dysgraphia and CAPD, I would wonder if this is a working memory deficit (often a primary deficit in dysgraphia, secondary deficit in ADHD, and a frequent confound with CAPD).
Sorry, this probably did not clear up anything for you...
