When teachers work in isolation, they tend to see the world through one set of eyes ─ their own. The fact that there might be someone somewhere in the same building or district who may be more successful at teaching this or that subject or lesson is (A) based / lost on teachers who close the door and work their way through the school calendar virtually alone. In the absence of a process that (B) allows / forbids them to benchmark those who do things better or at least differently, teachers are left with that one perspective ─ their own. I taught various subjects under the social studies umbrella and had very little idea of how my peers who taught the same subject did what they did. The idea of meeting regularly to compare notes, plan common assessments, and share what we did well (C) mostly / never occurred to us. Rather, we spent much time in the social studies office complaining about a lack of time and playing the blame game.