Putting things together from scratch is why they make these mistakes. Consider how many students they have, how many preps, etc. No, teachers aren't perfect. Students forget this. A lot. Seriously, my students are shocked to see me out in public. They forget that I exist outside of school. Take into consideration how much time a teacher puts into their job. They get there before the students, stay later than the students, have coaching jobs, and families of their own, and they still have to take work home each night to grade and plan. Yes, it is the profession teachers decided to go into, but that doesn't make it too much better in the end. Mistakes happen. It is a part of learning. We see what we think we typed, just like anyone else, and it is not until later that we realize it...after we have made 50 copies. It would help if we had a proofreader besides ourselves, but tell me who is willing to do that? On my tests I sometimes make a mistake, but I own up to it and let the students know. I never count it against the students and I give them additional time if needed, even if it is on an individual basis after school if necessary. I also don't count off for certain errors because I take into consideration the amount of time and lack of editing that comes into play when testing. However, that said, I do expect my students to know when to use basic mechanics and how to spell vocabulary words.

TLDR: Teachers are human too, get over it.