Do I have to show my work on every problem?  (Monthly practice work and on tests)
Uh...yeah.   Well, if you want to do well in math, that is.  There are two basic reasons why showing work--almost every step--is really vital in math.  More musing about it following the two reasons.    
  1. To avoid little mistakes.  Too many times students do steps in their head, and such as subtracting 17 to both sides of an equation, but actually add instead of subtracting on one side---and if they had actually written the -17 on both sides, their brain would have realized that it was subtract, not add...and the student would not have lost 3 or 4 or 8 points on a test.  Just a few of these kinds of a mistake on a test and all of a sudden an A grade has turned in to a C, or a B grade has turned in to a D. 
  2. Checking answers: