One of the reasons math is painful for many is owing to our insistence on `worshiping' the `goods sold by weight' zombie, AKA, the avoirdupois system.
Almost every child knows how to count money. Our daughters knew just how much I'd pull from my pocket, before I had a chance to check, not long after they started to walk. Decimal systems are easy to get down cold in a hurry ( have .70 of a dollar well, where's the other .30?).
The metric system (SI) is a decimal system.
Compare: 1000 m = 1 km vs. 1760 yd. = 1 mile (or 8 furlongs or 320 rods, and each rod made up of 5 1/2 yd.). So, kids get to learn how to lick at and tickle (so to speak) the `king's foot' in all units of measure/dimension and only then are introduced to SI. It should be the other way around and the latter only encountered in history class as a footnote.
For parents and particularly students having troubles with the whole subject I'd suggest running down all of Isaac Asimov's series on math (Realm of Numbers/Algebra/Measure) and his Understanding Physics (compilation of three volumes). He wrote clearly and with a sense of humor, gives straight forward examples and you should be able to find used copies cheap.
well, that's a `partial fraction' of my opinion