I thought I was smart as a kid. Always did better than anyone else in school at math. My mom used an abacus daily in all her calculations. She would challenge me at computing answers to math problems, I with pencil and paper, my slide rule or just using my head, and she with an abacus. I never could win against her.
I wouldn't allow my kids to use calculators or computers, as the old-fashioned methods sharpen ones mind.
I don't know what they teach children in school. Without a calculator most high school grads can't make change.