We teach math linearly, because we follow the child's brain development.
numbers are quite an abstract things, and proportion is even more so. the next step, the percentage, add relative point of views too. you just can't teach that to a child that literally can't tell his right from his left.
Well, you can, but he won't really understand it and it is effort down the drain.
So I know that here we all are CS/EE/whatever, and probably knew more math then our elementary school teachers, but there is a reason to these steps, even if the said teacher never know about it.
