I worked in a school last year tutoring reading, basically as a volunteer (I was hardly paid anything). I worked with kids one-on-one every day. Not a single parent sent in a note or a card saying "thank you." NO holiday cards, end of the year cards, or anything of the like. It was really depressing. By the end of it I was thinking "Figure out your kids' problems on your own." It's different with teachers because they are actually paid (and paid well in our district). But I imagine that the good ones don't get a lot of feedback. I have told DS's teacher multiple times already that I'm thankful for what she's doing.