Absolutely! I have a dd who had issues with visual tracking as well as other vision challenges and when she was tested with the WISC (not WPPSI) she scored extremely low on Block Design vs the other subtests (with the exception of Symbol Search, which also relies heavily on vision).
I would look at two things - how much lower was the Block Design score? If it is more than 1.5 SD that's considered significant (15 points = 1 SD on the WISC, I'm not sure about the WPPSI) ; on the WISC-IV that might bring the PRI score and FSIQ into question, but I am not familiar with the WPPSI so can't help with it.
I also wouldn't assume your ds is going to outgrow vision tracking issues - our dd didn't! We didn't even realize she had them until she was 7, and she needed vision therapy to get past the tracking/etc issues. Vision Therapy was *really* successful for her, but her tracking/etc issues were due to weak eye muscles, and eventually after a few years the issues reappeared and she had to go through another round of vision therapy. If your ds hasn't been evaluated by a Developmental Optometrist, I'd seriously consider it.
Best wishes,
polarbear
