I teach in a school with multiple parallel classes. Results from the different classes are ALWAYS different, because no two classes are identical, not because the teachers are of different quality. One year I may have great-looking results, the next year another class might have great-looking results.
However, as standards of teaching and learning within the school are closely monitored as a previous poster outlined, SLT have the ability to analyse the results, to look behind the 'headline data' and review the performance of each class in full knowledge of the context.
Whereas publishing 'raw data' on class performance to a wide group WITHOUT the ability to see behind the data can just lead to misunderstandings at best or, at worst, witch hunts against particular teachers.
In the course of a reasonable length teaching career, I have had parents complain about me, and have had parents write letters of congratulation about me. Each complaint hurts, of course, and each has been fully investigated and found not to be substantial or, most often, a question of perception - for example, a pupil might claim 'Ms Can't hates me', on the basis of being told off for a misdemeanour that they could reasonably expect to have been told off for. I, and all the colleagues I know, agonise and soul search when these situations arise, but in a profession all about interactions between people, perception can be very powerful both for good and ill.
The only advice i would give is not to pre-judge, and in particular to encourage your child not to pre-judge, as starting off from a perception of 'Ms X is awful' predisposes a negative perception of many otherwise neutral events.