We all know that teachers aren't perfect, and certainly, we all make mistakes, including typos. I think the difference, particularly in the OP's case, is that the mistakes are on typed papers that are coming home. All teachers (in every subject matter, but especially English teachers), should proofread materials before hitting that print button. Many of the mistakes mentioned in previous posts (kindergarden, for example) would be caught with a simple spell check. If misspellings and incorrect grammar are sent home often, concern is warranted, and I say this as a parent and former teacher.