Calliope knows her marks in certain subjects are lackluster at best, but for her to suddenly skyrocket up to a perfect or near perfect score would raise far too much suspicion. So she would memorize the gist of a few answers, just enough to get her from a failing or barely passing mark to a comfortably passing mark, and then Evanesco it into oblivion (consider Incendio-ing it away but just in case ashes could be fixed with Reparo or some other spell...she would eventually talk herself down from that option).

What would your student age character do if their wand broke during OWL/NEWT examination week?