I remember the “ban calculators” back in the day US math scores have hit a low point in history, and calculators are partially to blame. Calculators are good to use if you already have an excellent understanding of the operations. If you start learning math with a calculator in your hand, though, you may be prevented from developing a good understanding of numbers. There are ‘shortcut’ methods for basic operations that are obvious if you are good with numbers. When I used to teach math, I had students who couldn’t tell me what 9 * 25 is without a calculator. They never developed the intuition that 1025 is dead easy to find in your head, and that 925 = (10-1)*25 = 250-25.