Common Core Considerations...
The question in the title is appropriate for which grade levels?
Which of your students/children
Think fast--get it right? wrong?
Need to write it out?
Need a clearly taught method?
Need less repetition? Extensive reps?
How do you make a variety of thinking/learning styles work in a collaborative setting when one of the children in a group thinks
15+55=70=1 hr + 10 min
Do YOU show them that adding 55 min can be done by adding 60 then "backing off" 5? OR
Do you ask THEM who found another way?
Yup, teaching is the easiest job....