Here are a few real-life scenarios that have nightmare potential for some science teachers: a first-grade teacher who has used the Rock, Sand, & Soil kit each fall for a decade, and has integrated it throughout her literacy instruction, suddenly finds out two weeks before the start of the school year that the kits are unavailable and that she will need to teach a unit on motion instead. A middle school life science teacher is told that because of declining school enrollment, he is being shuffled from 7th grade to 8th grade, where he will be expected to teach units on astronomy, oceanography, weather, and plate tectonics that he has not taught before. A physics teacher shows up to the faculty meeting the day before school starts and is surprised to be handed a schedule that includes one earth science class, which technically he is certified to teach, but has never done so. In each of these cases, teachers are put in situations where they may be forced to stay just a few steps ahead of their students. They must teach at the boundaries of their own knowledge. For some teachers this is invigorating, while others worry that stepping off the path of certainty carries the risk of being revealed as a fraud.