When I was in high school, we had to write a 500+ word composition for English class every week. It was due on Monday when you walked into the classroom, no excuses. Our teacher was very strict about grammar, spelling and punctuation. She had a list of mistakes that she called "F" mistakes, and if there was one anywhere in your paper, it was an automatic F. I don't remember the entire list but here are a few of them-- your, you're; there, their, they're, then, than; it's, its; where, were, we're; to, too, two etc.
Computers with word processors still weren't in every household around here back then, but later on, the same teacher had a poster she hung in the room that was the "Ode to the spell checker"