I don't think I agree. 3 + 5 = 8 isn't something you need to literally memorize, but if you don't memorize such facts of basic arithmetic you're at a disadvantage when it comes to doing homework and tests. It's easier and less error-prone to memorize 8*7 than it is to work it out manually every time you see it until it sticks.
For what it's worth, I struggled with math in elementary school and especially high school -- I failed algebra I, then passed it with a D; then I failed algebra II before passing it* with a D. It wasn't until I was forced to take a business calculus class in my 20s that it started clicking, and I assure you the quality of instruction wasn't any better at the college level than it was in high school. (I did eventually graduate with honors with a math degree.)
For what it's worth, I struggled with math in elementary school and especially high school -- I failed algebra I, then passed it with a D; then I failed algebra II before passing it* with a D. It wasn't until I was forced to take a business calculus class in my 20s that it started clicking, and I assure you the quality of instruction wasn't any better at the college level than it was in high school. (I did eventually graduate with honors with a math degree.)