This is difficult in my field. I teach English Language Learners. Students and parents will both have difficulty filling out a survey due to language issues. We can have the survey translated but many of my parents don't have much formal education and may not read well in their native language, don't always return things sent home from school, don't feel they have time, etc. I dont' think I would get enough responses to get a true picture.

Student input can be really valuable, but certain precautions need to be taken to protect the teacher from unfair negative judgments.  For example, I have seen great teachers get bad reviews from students who were frequently absent, were zoned out when physically present, didn't complete assignments, or turned in poor quality assignments and expected to get good grades for simply bothering to do them. Then they stated things like, "I didn't learn anything in this class" or "The teacher didn't explain the material."

Teachers with the highest and lowest standards tend to get the most negative criticism.  Before answering questions about the teacher, students should be "primed" by being required to first answer questions about their own behavior (e.g., their attendance, assignment completion, level of effort in and outside the classroom, etc.). Teachers also need some protection from the negative effect of institutional issues that they don't have control over (e.g., access to technology/equipment, physical aspects of the environment, scheduling, etc.).  Some students rate a course or teacher poorly because they found it too hot or too cold in the room or because the class was too early or late in the day for their liking.  Questions about these things should also be addressed prior to rating the teacher so the student can get it "off the chest" and to help them separate out the elements that are affecting their perceptions.

There should also be a comment section where students can say something in their own words.  Here is where you often find out if ratings are based on things outside of the teacher's control, or whether there are specific actionable things the teacher can do to improve students' experience.  It also gives a space where an evaluator can learn that a teacher had an especially positive influence on a student's learning or attitude towards learning a la, "Math never made sense to me until, Teacher X did..."

Parent input can follow similar principles, but should be an entirely different document from the student feedback form.  But the parent form should encourage them to review the student feedback prior to responding.