When I say calculations I mean doing algebraic manipulations, not arithmetic. I have a strategy: first it try to do it mentally, if I can't I start doing it on

When I say calculations I mean doing algebraic manipulations, not arithmetic. I have a strategy: first it try to do it mentally, if I can't I start doing it on paper, then once I solve it I wait for a long while and then I do it mentally. My impression is that that kind of thing isn't really taught and I believe it needs to be taught.