Ability to work and play alongside other people, even people not exactly like themselves. Good numeracy and literacy. In particular not being fightened of STEM subjects. I'm a school governor to help make education better for my kids and those around them. Many of my relatives went to (very well known / pricy) private ("public") schools and I wouldn't consider anything other than a local normal school for my kids, no…
> Ability to work and play alongside other people
I find the best way to do that is to have more than one child. Siblings have a safe place to practice basic and advanced human interaction every day wether they like it or not! Helps a lot in the long run.