Splitting numbers to add just means to decompose the numbers along the ones, tens, and hundreds, and then add the different place values. The numbers can be written horizontally, vertically, or separated by arrows.
|Number Splitting Across|
|Number Splitting Down|
Some teachers like the across as it seems a little neater, while others like the down method as it’s closer to the standard algorithm.
I prefer a slightly less structured method where students aren’t required to organize their numbers quite as much. Even if it gets a little sloppy, you just need to track where the numbers went and what they split into by following the arrows. When I want to get organized, just move to the partial sums algorithm.