This is my new favorite word! Asking kids to justify their learning leads to deeper learning! Asking teachers to justify their learning leads to better teaching!
If I simply need the answer to a math computation problem, I can use a calculator or I can ask Siri. If a kid needs an answer to a math computation problem, the kid can also use a calculator or ask Siri. Regardless of how the kid gets the answer, explaining why it is the correct answer makes it powerful.
In math, we no longer need adults who can compute. We have tools for that. We do need folks who can solve never-before-seen problems.
Do kids need to know how to compute? Absolutely. Will that ability lead to a productive future? Probably not. Kids need to turn the ability to compute into deeper problem solving! That only happens when they talk about it!