[imzadi]

Arithmetic doesn't require any sort of critical thinking at all, so the point is moot. Advanced maths do, but those aren't usually taught in K-12; however, not getting those critical thinking skills young can make it more difficult in college to apply what you've learned to more complex problems. I'm speaking here as someone with a math degree who tutored college level mathematics for 3 years.

As to the other point, you're right that many teachers don't encourage critical thinking or individualism. That's a fault of those teachers, and of our society that tends to frown on questioning authority.

All that said, kids who only socialize with their own family and maybe their neighbors don't develop the skills that come with having their views challenged and needing to defend them.