I think that it can be very, very difficult to adapt when your child starts in full time school. I know that I found it very difficult when dd started.
I think the problem is that we all want the very best for our children, and obviously we have very stong ideas about how best to raise a child! And we all have different ways. Not right or wrong, as such ,but different.
The difficulty is that when a child starts school they will be in with possibly 29 other kids, all of who's parents want the best and will have different ideas as to how to get a child to be happy and 'socialed'.
With the best will in the world, I don't think any teacher, no matter how good, can statisfy everyone 100% of the time. It simply isn't possible. For every parent annoyed at a child being told off for something the parent thinks is unreasonable, there will be another parent annoyed with the teacher for not doing more if, say their child has been hit. You only have to read Mumsnet to see that this is the case.
What sometimes worries me is that often the first responce of the mother is to be very angry and go in all guns blazing (not saying that this is the case this time btw). I don't think that this ever going to be helpful.
In the end, we need better resourced, smaller schools. If we need to direct our anger I think it is better put in other directions than always the classroom teacher. Sometimes that teacher can be out of order, and then you need to take things further. But the bottom line is that it is unreasonable to expect a teacher to cater to the diverse learning needs of all the children in her care, and to dicipline them all differently, to use different stratgies with each and every child, and set different rules each time to suit the family stance of standards. In the end, if that is what you want there is only one possiblem solution, and that is to home ed.
I know that this conversation has been about primary, but we have had similar discussions about secondary. I teach 194 different kids this year. I can't be their mum, they already have them and most of them are excellent. I can only be their teacher.