From day one, our first and foremost class norm is "Our reasoning is more important than our answer." This unfortunately, for many, goes over like a lead balloon. This is my first year that I've made this norm as explicit as naming it every day.
I can count on one hand how many of my math teachers explicitly enforced this idea through encouraging such work ethic via their rubric/grading. That alone was enough for a later instructor's motto, heard at least twice a week for the 3 years I had him, to resonate: "a problem well-defined is a problem half solved." For those it sticks with, I can assure you it will be worth it. It was for me, at least.