Math With Bad Drawings had a nice post about strategies teachers can use to address a student who volunteers an incorrect answer. This is a natural dilemma for teachers who want to encourage class participation but who don’t want to deflate students who make mistakes. I recommend this essay highly: http://mathwithbaddrawings.com/2014/11/05/wrong-but-not-stupid-or-how-to-call-out-mistakes-without-trampling-the-mistaken/

One recent strategy that I’ve employed is quoting the trolls from Frozen: https://meangreenmath.com/2014/06/14/a-bit-of-a-fixer-upper/