One minor confound is that the difficulty of each new fact isn't identical. While going from 10 to 11 requires learning 11 new facts, 9 of them follow an easy p

One minor confound is that the difficulty of each new fact isn't identical. While going from 10 to 11 requires learning 11 new facts, 9 of them follow an easy pattern (11 x n = nn), and the 10th you get for free with decimal notation. That leaves only 11 x 11 = 121 to be memorized individually. Oddly I don't think I ever memorized the 12 x [0-9] case myself. It's quick enough to recover it from smaller numbers (12 x 7 = 70 + 14) that I just did that in school, and memorized only 11 x 12 and 12 x 12.