if you arrived for work each morning and:
greeted your boss with a 'hallo' and every morning got dismissed with a wave of the hand and told to 'go away, i'm busy'...how would you feel?
if your boss constantly accused you of lying...how would you feel?
if your boss dismissed any concerns you had and never addressed them....how would you feel?
if your boss behaved with no respect or manners and felt it was perfectly fine to keep polite behaviour for visitors but was a complete stresshead to you....how would you feel?
i suspect you would feel like crap every day
now imagine this is not a boss but a teacher of 30 impressionable children (and you have seen some of this behaviour yourself and heard the same from your child's classmates)
your child greets their teacher nicely each morning (because that is what they have been taught by you) and never gets the same polite greeting back
your child tries to tell their teacher something is missing etc (because they have been taught by you that an adult is who to go to) but gets told they are wrong
your child tries to tell their teacher they are injured (because they know that a parent would be sympathetic and have a look and administer the relevant treatment) but gets told 'no you can't put a cold compress on your foot' (that a friend has just landed on twice in PE) or that a classmate is being nasty to you but despite your teacher telling you they will do something about it, they don't
your child sees their teacher being perfectly lovely to parents but never sees that behaviour within the classroom (and you have taught your child that within the confines of your home you can let your stresses out but in public you should always 'bite your tongue etc)
i suspect your child would feel like crap every day
now i am not an idiot, i know 30 kids are a handful, they can whine, they can not look properly for something, they can be telltales, they can be rude but not all of them and not all the time...children respond to what you give out...give them stress, they will end up like you (if 30 kids stress you out, get another job)...give them patience, respect, time and trust and they will give that back to you
any wonder we are reverting to homeschooling?