I sub at the high school my child attends. Last year, I taught the entire year as a long-term sub. She was in my classes, which was actually really great! But now the teacher I was filling in for is back.
When I sub there now, I invariably get comments from the students that "I wish you were still teaching", "I never understand Teacher X", "Teacher X talks too much and doesn't teach us what he's testing us on."
I see for myself, when I subbed in X's class, that they are far, far behind where I was last year, and will never be able to cover the required material by the end of the year. (Which, because we are on a 4x4 block schedule, is in three weeks!). My child is now taking a class from X, and complains frequently that she has to explain things to her classmates, and that they are often left to decipher the textbook alone.
As a parent, it infuriates me that X is allowed to teach in this manner. As a teacher, it frustrates me to no end to know that, because X has been at our school for a certain number of years, he will continue to teach this way, while other, more effective educators, sit on their hands and are unable to do anything.
When your teen-aged child, who thinks you are the uncoolest, geekiest parent on earth, tells you "You are a way better teacher than X" you know that means something!