I have made it a goal this year to find one student in my classes who can work with numbers fluently, and discuss number concepts clearly, without needing to resort to a calculator. It is just five months into the school year, but I have not found that student yet.
Number sense seems to be an "endangered species".
Today's youth probably have very little, or possible no, conception of that to which I refer: it's difficult to miss that which you have never had. That does not lessen the danger that this poses for the future of our youth.
I have repeatedly had students reach for their calculators in order to add zer0, multiply by 1, calculate 2 times 10, and other such basic calculations. Dividing by 2? Forget it!!