If your kid says to you, "The reason I don't get math is because my teacher never goes over our homework, and I don't even know whether my homework is right, because my teacher never corrects it," then you will probably feel a slow burn of outrage. How can any teacher be so lazy?
But, if the same kid has been issued, in addition to a text book, a solution manual to the text book, you might want to ask her (or him) why she isn't correcting her own homework. You might want to stop for a minute, and imagine 120 kids just like yours diligently practicing factoring limit problems (just as yours does). Even if they only have about 25 problems a night, you will soon see that the result is 3000 problems. No one can correct 3000 problems. A day. No one can circle in red pen just where each child went wrong on each of those 3000 problems. Every day. No one can write enough happy faces or stars on the ones that made no mistakes. On 3000 problems. Each of the days of the week.
Still, even if you don't know this basic fact of math teacher-hood, even if the quantity of homework problems doesn't occur to you, and you decide to take your outrage out on the teacher, and you decide to email her (or him) with your anger and your frustration, then, please, for the sake of your child, whatever you do, don't cc the principal.
Don't do it. Really. Your relationship with the teacher will be better. Your relationship with the principal will be better. Your child's relationship with the teacher will be better. The teaching will be better. The world will be a better place. There will be rainbows and flowers where before there was only sewage and toxic waste.
Just believe me, OK? I know what I'm talking about.