Multiple choice and checkbox type problems support a show_correctness="never" option in the XML, which many instructors find useful. A discussion of workarounds for this came up just today on the Tender help form, and the instructor was thrilled to learn about the show_correctness="never" option, which he hadn't been able to find in the docs. It works like this:
<choicegroup label="True or false: the earth is round." type="MultipleChoice" show_correctness="never">
I tried to point him at where to find it (I think it was in the old XML format docs?), but couldn't find it in either the Studio docs or the current XML docs. Here's where I looked:
Maybe it should be added back in to the docs? It's a useful feature. Here's today's help forum thread on this:
Search for show_correctness in the docs.