My youngest was highly imaginative and still is. When he was about that age, he lived a great deal of the time in fantasy. I recall being asked frequently by strangers what level he was in martial arts only to have tell them he was dueling light sabers in his head, not practicing moves of any sort. I made sure all of us told him frequently what was real and not real, but I do think the lines were blurred for him for a while. He grew out of it with time.
And you're right - some teachers will value the creativity while others will find your child less than their ideal student, but that is likely true for amost all children. It is rare when the teacher's reaction to your child becomes a truly destructive environment. We've had it happen twice - once we rode out and helped our child learn how to cope and once we moved him to a different teacher. But there have also been teachers who have said that it was a joy to teach our son, years where he thrived. So it really is like a box of chocolates.
Then again, I used to have an imaginary friend who had a seat at our kitchen table and spent hours listening to all of my stories while the two of us were on the backyard swings. Thinking back, it was pretty sweet to have a friend that let me do all the talking.
