This made me smile. Ran up against similar issues when visiting a class as a school governor.
Yeah, when I did classroom work I checked. One slip and there goes your credibility. Actually, I used to tell my students that every time they misused an apostrophe a fairy would die.
lol!! Yes indeed - like the one I used to use on my children - if the music's playing, the van has run out of ice-cream...
Parents really ought to return letters & teaching materials with the errors circled in red, marks given out of ten, & comments. You know the sort of thing; "See me after school - please telephone to make an appointment." etc...
Some of the demi-literate guff that issues from our local schools almost make me sympathise with the homeschool brigade...