I have made a lot of mistakes teaching writing primarily jumping into elementary school lessons without properly reviewing what I was doing or why. Young writers will rarely do more than list or explain.
Misspellings are common use the errors as handles on what to teach.
Watch your attitude and the spirit with which you correct errors. Beginning in 4th grade students can probably describe an event or a room or a toy, for this is the least complex style. Students, even in middle or junior high school who have good writing ideas rarely develop them as fully as they might. Don't despair if the writing sounds pedestrian. Their minds and hearts are a work in progress they can't produce what they have not taken in.