Elapsed time is one of the more difficult concepts kids have to grasp. See the examples below showing how we’re laying out a problem. There are other strategies that work for kids, so if you come up with something that works better for them, that’s okay! I’ve seen several good methods in class including as Faalele’s and Alexis’s.  

Elapsed time can be done using subtraction, but it causes some hitches for kids so we focus more on “adding on.”

Here are several examples. # 1 is the traditional method of adding on; #2 shows the traditional method with a twelve hour jump.  Picture #3 shows how straight subtraction only sometimes makes sense to kids. Finally, #4 depicts a problem where you’re just backtracking. In this case, subtraction is appropriate.