But I doubt they will ever be able to make it so fair.
I think it's absolutely impossible. For instance, I work with one teacher who is frankly embarrassingly incompetent. She doesn't know anything that isn't in the textbook, but because she's incredibly nice (and her subject isn't tested), parents and pupils love her. Her lack of knowledge is excruciating, and she has little interest in the life of the school, but her 'performance' is high.
Pawian, how do you handle cheating during tests in the classroom? My policy is this -
1st class - paper torn up (for dramatic effect) and a big fat "F" given to them on a A4 piece of paper. Usually does the trick, and after one gets caught, they won't cheat again for a while. They get to do it again in peace, and normally I'll find them during the normal school day to come and do it again. I'll tell the parents, but always with a "please don't give them into trouble, let them discuss it with you first" comment.
2nd/3rd class - paper torn up and parents informed. No consequences, but they have to come and do it again after school.
4th class - paper torn up, parents informed and a mild telling off about what they've done. They also need to come and do it again after school.
5th-8th - paper torn up, parents informed, and a severe lecture about not doing it again. They don't get to do it again, it just gets counted as a 1. They also have some punishment homework, which usually gets picked to bring them some suffering - for instance, having to learn and act out a short piece for the rest of the class.
I'd personally rather not give classes 1-3 any tests at all, but stupid parents...