And of course the student has to be at least somewhat motivated. Computer programs are NOT repeat NOT sufficient as teachers. They are good, but like any other book in the world, you get out of them what you put in. Copies available at cost if you're interested. Never, never, never teach magic mystical spells that involve taking a number from here and putting it over there and multiplying this and subtracting that and shoving the answer thataway and inserting a decimal point somewhere.
Numbers are real and tangible things.
The symbols on the page are hieroglyphics, and manipulation of hieroglyphics varies from weak to useless to actively damaging. And so on.