Thank you.
I absolutely detest the increasing number of writers who think you need to use an apostrophe any time there is a "s" at the end of a word. It doesn't surprise me that there were such mistakes on a PTA poster. As a former writing teacher, I loved teaching my kids how using appositives, dependent, and independent clauses made them better writers. When done with the intent of teaching them to be able to express themselves better, they ate up the grammar teaching, just as Veronica describes.
It hurts my eyes to read some of the posts on TE. I know that using apostrophes incorrectly is not a sign of a personality deficiency, but... I guess I am old fashioned; I still proof my posts, even though this is not what I call "formal" writing.