I did a debate on this awhile ago and I'm interested to see what other people think. The current system is based on test scores of students and principle reviews. Both are important, but very weak forms of evaluation alone. Student evaluations are criticized because many believe students will essentially "punish" their teachers for giving them bad grades. However, studies have proved otherwise. In fact, teachers with positive reviews generally got six months more teaching done than ones with lower reviews.
Administrators can only know so much about a teaching style and the impact it has on the students. For 180 days (in most American public schools), students attend the class and see their teachers on a daily basis. By the end of the academic year, students generally have a good grasp on how the teacher teaches. By instituting student evaluations, it would help the school weed out inept teachers, keep the excellent ones, and improve education here in the U.S. as whole.
Students definitely know their teachers better than anything else, so they should be able to have a say. I have had numerous teachers that had no clue what they are talking about, but still have a job. Once I had a horrible chemistry teacher (so bad that other teachers gossiped about him) and I got an A in his class, though I understood absolutely nothing. The next semester I had a great teacher and understood everything perfectly and got a B (because I never did the homework). Grades should not have too much to do with teacher evaluation because of this, and students can give you details about what they are doing wrong. Of course, students are extremely critical and can exaggerate, so complaints should not be blindly accepted. Teacher evaluators should look into them and see if they are true. Then they may be able to alert the teacher to their mistakes. If the teacher doesn't fix them, they should then be fired. It can absolutely be a great system and I know high schoolers would love to be able to have the power to help weed out bad teachers.
I wouldn't want a high school student telling me how to do anything because they are immature and under educated. Not to mention that they may become socially charged and take that out on a good teacher.
I do not think that the current system is working but I also do not think that high school students should be evaluating an adults position.