I worked for a long time on number sense. Adding and subtracting took FOREVER!!! I was supposed to do that, perimeter, area, time and elapsed time, and multiplication arrays. Anyone else think that was a lot? Well, I got through addition and subtraction and time, and area is next week.
To teach subtraction, I came up with some activity sheets that teach subtraction in a non-traditional way. Many of my students came in knowing how to borrow, but they struggled to do it correctly and didn't know why they were supposed to do all the steps. Some of the sheets used Singapore methods, while others used number lines or hundreds charts. Either way, I think my students truly understand what subtraction is and not just the rote process for subtraction.
this unit and all of them are available at my TpT store.