Thanks so much to everybody for the support and kind advices! I have been neglecting the issue because I didn't realize that he could actually have vision issue this early! And you made great points too about potential reading problems and test scores problems. What the test revealed was that he seemed to have scanning issues, hence the hypothesis about vision problem. I googled it last night and it seems that if a child has vision issue, block design is the only score that is not likely to be impacted, since he won't need to distinguish fine lines between shapes. I will check our local pediatric ophthalmologists and ask if he needs glasses. I am a bit sad that he is not avoiding our genetic "defect", but as both parents wear glasses, it is not likely that our kids will be spared.
