These are important whether positive or negative things happened. Gee, you're concerned that perhaps this teacher does not quite understand your kid's needs because he said x and y. Then if follow through doesn't happen you write again, as well as any meetings, etc. Make yourself a template for these letters so you can just crank in the details and fire them off. If not, they are very important for steps you may want to take later.
Second grade reading level is pretty restricting, and there are ways to bring it up.