Unfortunately not all teachers are effective in their task to educate students. Nonetheless teachers need some form of evaluation, of course it should not be ranked on just one thing but rather a variety. Student achievement should rate heavily since that is what determines how successful the teacher was in giving the information to students.
Teacher evaluations should be taken into consideration how well the students are doing and if they are achieving well in school. If the students are not learning anything than obviously the teacher is not doing their job right or is not trying very hard. We should look at more than just how they act in the classroom.
There are many difficulties in the classroom. Some schools have so many disruptions and are so unorganized that the teacher does not have a fighting chance. There should be different scales according to how well behaved the students are at a particular school. Someone from a high performing school should not be judged the same as one from a poor performing school.