You've got to be carefully taught
Some people go into teaching because they genuinely like children. And some, I think, become teachers because they like to push people around and children are easy.
Combine the bully with the peever, and you wind up with a pathological case like the one described by Stan Carey in his excellent blog Sentence First: the Irish teacher in the 1950s who scissored out errors from student papers and required the students to take a shovel and bury them out behind a shed.
Though this is an extreme example, I suspect that there are many pedagogical malpractices connected with writing and English usage. There is, for example, the model requiring that students write paragraphs of five sentences each. There is the anecdote in Eudora Welty’s memoirs about the teacher who stood at the door to the restroom and refused to let the girls out until the miscreant she had overheard say “might could” confessed.
Surely some of you good people could recount similar examples. I don’t mean the routine superstitions about not splitting infinitives and not putting prepositions at the end of sentences — there appears to be no end to that nonsense — or the misplaced reverence for Strunk and White “rules.” I mean outrageously bogus practices and disproportionate punishments. If you feel like sharing, please deposit your accounts of outrages below.