Even though I chafed a bit at the delays it imposed and kept asking the teacher about other more advanced topics, I do not regret a single minute of the time spent chanting 12-times tables in my first couple of school years. Same deal for written exercises and homework - I don't think I'd be so good at mental math, estimating, and 'back of the envelope' calculations done in pencil if it weren't for all that practice as a child.