What's monumentally moronic is that a tiny subset of teachers still try to use this line, here and now, in AD 2023. It was still quite highly moronic in the years of my school career, which was happening just on the cusp of the computing revolution -- which everyone at the time with at least one functioning brain cell could see looming in all its inevitability just about 6" over the horizon.

Outside of basic arithmetic this canard doesn't really hold water. Understanding how to add, subtract, multiply, and divide arbitrary numbers without a calculator is, of course, essential. But once that's understood, it's really unnecessary to have to stop to figure out by hand whatever the fuck, say, 23 divided by 4081.75 is when it's just one component of some greater problem. In that context, using a calculator is not a "cheat," even though some educators to this very day cling to the belief that it is. If you are doing algebra, geometry, calculus, etc. it's really pointless not to use a calculator for the tedious small stuff, because if you don't have an understanding of the mechanics of the problem you're not going to accomplish jack squat... calculator or not.

(Yes, nowadays there are fancy graphing calculators and computer software that can do algebra, trig, etc. for you. You could probably even ask ChatGPT and have a nonzero chance of it getting it right. But back in my day we did not have them, because they were not commonplace, not very capable, and still extremely expensive. And computer software be damned, it was not quite viable yet on a middle or highschooler's budget to carry a traditional computer with you.)

Sure, I still have the skills to get out a notepad and do a long-division-with-decimals calculation by hand, even in my adulthood when no one has asked me to in decades. But you know what? No one has asked me to in decades. So I'm not going to do that standing in the grocery aisle with a 12 pack of something in my hand, or standing over the milling machine contemplating where to drill the hole in the $1200 piece of material. In the former case I'm going to round off and make an accurate enough assessment for casual purposes, and in the latter case you bet your ass I'm going to get out my calculator or phone.

And yes, I had teachers in high school who absolutely did force us to calculate multivariable algebra or geometry equations without a calculator and screech "SHOW YOUR WORK" at us, which explicitly included all the long multiplication and division and shit, when in reality just simplifying the equation and then solving for X, Y, Z with a calculator would have been just as correct and infinitely less irritating. And no, they did not do this for any other reason than the ironclad belief that if students were not being forced to comply with arbitrary rules and tedium in complete contravention to logic, they were not "learning." That was considered "cheating." As it turns out, the point was not to inform. Rather, it was to have an arbitrary and illogical standard to use to berate and punish children. The only thing that was being taught was not to attempt apply logic or speak up, but to submit to authority unquestioningly... or else you get a zero and/or a browbeating/detention. It was bullshit then, it's still bullshit now.