All great reminders that what we do every day is appreciated by someone at some point. They often don't tell us out loud, they may even act completely nasty as they push us away, especially in middle school. One thing I have learned over the years is to not take it personally when that happens. It's almost never really about the teacher. It's usually about something else: feeling inadequate, some friend drama, family problems.
Teaching is weird in a way: you put all this work in, and you often won't know the end results. We just have to keep on doing what we do, knowing that we are affecting and influencing kids' lives every day, whether or not we are thanked for it.