You don't need to know that.....

...but isn't that wonderful that you do! While preparing for an annual syllabus exam, my student began demonstrating chord progressions in keys he wasn't required to know yet.  My first response was to tell him not to worry about them. Then I almost bit my tongue and began praising him for how well he applied what he knew about chord progressions and asked him to show me more that he had figured out.  I realized quickly I wasn't wasting precious review time, but rather he was showing me how well he was understanding the theory he had been taught.  While discernment does need to be applied, I hope I can stop myself again when a student wants to deviate from what I think is necessary at the time and encourage exploration of their interests and accomplishments!