I wouldn't even read the PSI or WMI as low scores, per se. While they are lower than the other scores, they are still well above average and I wouldn't worry terribly about the discrepancy unless you are seeing functional difficulties IRL.
I'm wondering about the pieces where the tester noted that he hit the ceiling as well. I might ask for more info on that unless you already have it. Generally, I've not seen a child to be noted to have hit a ceiling until s/he has 18 or 19 scores. I could see a 17 maybe being a ceiling if there was a pattern of one missed, one correct until the end of the possible problems, but I'd see a 16 as less likely to be that type of pattern. My youngest had some of those "miss one, get one right" type of patterns that did deflate overall scores and, for her, I'm not sure if her ADD played into that or if she's just very asynchronous.
