How stupid can they be though? I remember my class and me being taught and mastering this in a single day when I was in second grade. Like the teacher broke us into groups, we learned how the numbers go in increments of five, etc., then took a quiz, and that was the end of it. A very short lesson that sticks with you for life, like tying shoes.
Kids don’t tie shoes any more. It’s mostly velcro and sippers now.