My Algebra 1 kids taught me lattice multiplication the other day. I'd seen it before but never understood it. I gave my tablet to a girl during class and said, "Teach me." It took her a little convincing to make her believe me, but then she did it.
This is my old-school version of multiplication on the left with Kaitlin's lattice multiplication on the right. I was skeptical that it would always work, but in breaking down what goes where and what gets combined with what, it does work. The sad thing is that the kids don't really get why it works. Lattice multiplication doesn't show the place values that you're using - at least in such an obvious way, I guess.
Oh well. I'm just happy that they can multiply! (On paper. I'd like to keep the other kind of multiplication out of the classroom. Though I did find out last week that I have a student expecting sometime this year.)