This is hugely anecdotal, I can find examples of both extremes and everything in the middle around me. I think its rather good/poor parenting, parents not havin

This is hugely anecdotal, I can find examples of both extremes and everything in the middle around me. I think its rather good/poor parenting, parents not having enough time to raise kids properly (hint: there is never 'too much' time you spend with kids, especially young), dumbing kids down with primitive addictive screen fun or social media. Lacking a lot of social interaction can make otherwise smart kids appear... less smart, since they may be shy, lacking motivation or skill to express themselves so they can be interacted with on higher level. Once you filter all of this (and probably much more), and still see a difference on massive scale, we can start having a case.